A long-feared Russian invasion of Ukraine appeared to be imminent Monday, if not already underway, with Russian President Vladimir Putin ordering forces into separatist regions of eastern Ukraine.

A vaguely worded decree signed by Putin did not say if troops were on the move, and it cast the order as an effort to "maintain peace." But it appeared to dash the slim remaining hopes of averting a major conflict in Europe that could cause massive casualties, energy shortages on the continent and economic chaos around the globe.

Putin's directive came hours after he recognized the separatist regions in a rambling, fact-bending discourse on European history. The move paved the way to provide them military support, antagonizing Western leaders who regard it as a breach of world order and set off a frenzied scramble by the United States and others to respond. In a lengthy televised national address announcing his recognition of the rebel-held areas, Putin railed against Ukraine as a failed state and "puppet" of the West, repeatedly suggesting it was essentially part of Russia.

Western powers reacted swiftly to Monday's decision by Putin to recognize the independence of the two self-proclaimed republics, the Donetsk People's Republic (DNR) and the Luhansk People's Republic (LNR), condemning Moscow. The leaders of France, Germany and the United States condemned Putin's move as a "clear breach" of the Minsk peace agreements. French President Emmanuel Macron, German Chancellor Olaf Scholz and U.S. President Joe Biden agreed that "this step will not go unanswered," the German Chancellery said in a statement published following their conversation.

U.S. Secretary of State Antony Blinken tweeted that Putin's decision required "a swift and firm response, and we will take appropriate steps in coordination with partners." The White House issued an executive order to prohibit U.S. investment and trade in the separatist regions, and additional measures – likely sanctions – were to be announced Tuesday. Those sanctions are independent of what Washington has prepared in the event of a Russian invasion, according to a senior administration official who briefed reporters on the condition of anonymity.

U.N. chief Antonio Guterres said Russia's decision amounted to "a violation of the territorial integrity and sovereignty of Ukraine and inconsistent with the principles of the Charter of the United Nations."

Macron, who was still pressing for a diplomatic settlement earlier Monday, called for targeted European Union sanctions against Moscow. His office determined that Macron is demanding the "adoption of targeted European sanctions."

U.K. Prime Minister Boris Johnson denounced Putin's decision as "a flagrant violation of the sovereignty and integrity of the Ukraine." A "very robust package of sanctions" would be triggered "with the first toecap of a Russian incursion or Russian invasion," he added. German Foreign Minister Annalena Baerbock said that Moscow was breaking the Minsk peace agreements that it signed in 2014.

"With its decision, Russia is breaking all its promises to the world community," she said.

EU ambassadors have been discussing a sanctions package on Russia consisting of four parts which could be agreed by the bloc's foreign ministers at a meeting later on Tuesday in Paris, an EU Commission source told Reuters.

The package, proposed by the EU's executive Commission, includes banning the trade in Russian state bonds in the European market and kicking the break-away regions in eastern Ukraine out of a free trade deal between the EU and Ukraine. It also comprises sanctions on several hundred members of Russia's state Duma who voted for the recognition of the break-away regions in eastern Ukraine, as well as on companies and banks involved in the financing of separatist activities in the these

NATO Secretary-General Jens Stoltenberg said Putin's decision "further undermines Ukraine's sovereignty and territorial integrity, erodes efforts towards a resolution of the conflict, and violates the Minsk Agreements, to which Russia is a party.

"Moscow continues to fuel the conflict in eastern Ukraine by providing financial and military support to the separatists. It is also trying to stage a pretext to invade Ukraine once again," he added.

European Commission President Ursula von der Leyen and European Council President Charles Michel, the European Union's two most senior figures, posted identical statements on Twitter. Condemning Putin's move as "a blatant violation of international law," they added: "The EU and its partners will react with unity, firmness and with determination in solidarity with Ukraine."

Serbian President Aleksandar Vucic said there are fears that the Ukraine crisis "could spread in other parts of Europe and the world, especially on the Western Balkans" and Romanian Foreign Ministry told all its nationals in Ukraine to "leave the country immediately!"

Japanese Prime Minister Fumio Kishida said that Russia's actions violated "Ukraine's sovereignty and territorial integrity and cannot be tolerated," while India's ambassador to the United Nations urged all sides to show "restraint" in the face of rising tensions.

China blames "complex factors." Beijing – one of Russia's closest allies – did not take sides, instead calling for all parties to "avoid any action that may fuel tensions," and Australian Prime Minister Scott Morrison slammed as "nonsense" Putin's claims that the troops being sent into eastern Ukraine were peacekeepers.

"We cannot have threats of violence being used to seek to advantage nations' positions over others," he said. "That is not a peaceful world order that would be achieving that. And so it's important that like-minded countries who denounce this sort of behavior do stick together."

Underscoring the urgency, the U.N. Security Council held a rare nighttime emergency meeting on Monday at the request of Ukraine, the U.S. and other countries. Undersecretary-General Rosemary DiCarlo opened the session with a warning that "the risk of major conflict is real and needs to be prevented at all costs."

The Ukrainian ambassador to the U.N. called on Russia to reverse its recognition of the two territories and return to negotiations, while Russia's representative accused Kyiv of planning to shell the regions and threatened "extremely dangerous consequences" to "militaristic plans" from the country's territories.

Ukrainian President Volodymyr Zelenskyy sought to project calm, telling the country: "We are not afraid of anyone or anything. We don't owe anyone anything. And we won't give anything to anyone." His foreign minister, Dmytro Kuleba, will be in Washington on Tuesday to meet with Blinken, the State Department said.

The State Department, meanwhile, said U.S. personnel in Lviv – in Ukraine's far west – would spend the night in Poland but return to Ukraine to continue their diplomatic work and emergency consular services. It again urged any American citizens in Ukraine to leave immediately.

The developments came during a spike in skirmishes in the eastern regions that Western powers believe Russia could use as a pretext for an attack on the Western-looking democracy that has defied Moscow's attempts to pull it back into its orbit.

Putin justified his decision in a far-reaching, prerecorded speech blaming NATO for the current crisis and called the U.S.-led alliance an existential threat to Russia. Sweeping through more than a century of history, he painted today's Ukraine as a modern construct that is inextricably linked to Russia. He charged that Ukraine had inherited Russia's historic lands and after the Soviet collapse was used by the West to contain Russia.

"I consider it necessary to take a long-overdue decision: To immediately recognize the independence and sovereignty of Donetsk People's Republic and Luhansk People's Republic," Putin said.

Afterward, he signed matching decrees recognizing the two regions' independence, eight years after fighting erupted between Russia-backed separatists and Ukrainian forces, and called on lawmakers to approve measures paving the way for military support.

Until now, Ukraine and the West have accused Russia of supporting the separatists with arms and troops, but Moscow has denied that, saying that Russians who fought there were volunteers.

At an earlier meeting of Putin's Security Council, a stream of top officials argued for recognizing the regions' independence. One slipped up and said he favored including them as part of Russia – but Putin quickly corrected him.

Recognizing the separatist regions' independence is likely to be popular in Russia, where many share Putin's worldview. Russian state media released images of people in Donetsk setting off fireworks, waving large Russian flags and playing Russia's national anthem.

With an estimated 150,000 Russian troops massed on three sides of Ukraine, the U.S. has warned that Moscow has already decided to invade. Still, Biden and Putin tentatively agreed to a meeting brokered by Macron in a last-ditch effort to avoid war.

If Russia moves in, the meeting will be off, but the prospect of a face-to-face summit resuscitated hopes in diplomacy to prevent a conflict that could devastate Ukraine and cause huge economic damage across Europe, which is heavily dependent on Russian energy.

Russia says it wants Western guarantees that NATO won't allow Ukraine and other former Soviet countries to join as members, and Putin said Monday that a simple moratorium on Ukraine's accession wouldn't be enough. Moscow has also demanded the alliance halt weapons deployments to Ukraine and roll back its forces from Eastern Europe – demands flatly rejected by the West.

Macron's office said Biden and Putin had "accepted the principle of such a summit," to be followed by a broader meeting that would include other "relevant stakeholders to discuss security and strategic stability in Europe."

U.S. national security adviser Jake Sullivan, meanwhile, said the administration has always been ready to talk to avert a war but was also prepared to respond to any attack.

During Monday night's emergency meeting, the U.S. ambassador to the United Nations, Linda Thomas-Greenfield, said Putin "has put before the world a choice" and it "must not look away" because "history tells us that looking the other way in the face of such hostility will be a far more costly path."

Putin's announcement shattered a 2015 peace deal signed in Minsk requiring Ukraine to offer broad self-rule to the rebel regions, a major diplomatic coup for Moscow. That deal was resented by many in Ukraine who saw it as a capitulation, a blow to the country's integrity and a betrayal of national interests. Putin and other officials argued Monday that the Ukrainian government has shown no appetite for implementing it.

Over 14,000 people have been killed since the conflict erupted in the eastern industrial heartland of Donbass in 2014, shortly after Moscow annexed Ukraine's the Crimean Peninsula.

Potential flashpoints multiplied. Sustained shelling continued Monday along the tense line of contact separating the opposing forces. Unusually, Russia said it had fended off an "incursion" from Ukraine – which Ukrainian officials denied. And Russia decided to prolong military drills in Belarus, which could offer a staging ground for an attack on the Ukrainian capital, Kyiv.

Ukraine and the separatist rebels have traded blame for cease-fire violations with hundreds of explosions recorded daily.

While separatists have charged that Ukrainian forces were firing on residential areas, Associated Press (AP) journalists reporting from several towns and villages in Ukrainian-held territory along the line of contact have not witnessed any notable escalation from the Ukrainian side and have documented signs of intensified shelling by the separatists that destroyed homes and ripped up roads.

Some residents of the main rebel-held city of Donetsk described sporadic shelling by Ukrainian forces, but they added that it wasn't on the same scale as earlier in the conflict.

The separatist authorities said Monday that at least four civilians were killed by Ukrainian shelling over the past 24 hours, and several others were wounded. Ukraine's military said two Ukrainian soldiers were killed over the weekend, and another officer was wounded Monday.

Ukrainian military spokesperson Pavlo Kovalchyuk insisted that Ukrainian forces weren't returning fire. In another worrying sign, the Russian military said it killed five suspected "saboteurs" who crossed from Ukraine into Russia's Rostov region and also destroyed two armored vehicles and took a Ukrainian officer prisoner. Ukrainian Border Guard spokesperson Andriy Demchenko dismissed the claim as "disinformation."

With fears of invasion high, the U.S. administration sent a letter to the United Nations human rights chief claiming that Moscow has compiled a list of Ukrainians to be killed or sent to detention camps after the invasion. The letter, first reported by The New York Times, was obtained by the AP. Kremlin spokesperson Dmitry Peskov said the claim was a lie and no such list exists.