As Ukrainians waved flags in a show of defiance of a feared Russian invasion, the United States reported that Moscow had added as many as 7,000 troops to forces stationed along the tense border – a warning that contradicted Kremlin declarations that military units were being pulled back.

A Russian invasion of Ukraine did not materialize Wednesday, as originally feared. But after a handful of positive signals from Moscow that eased tensions earlier in the week, the pendulum appeared to swing in the opposite direction again.

Western allies maintained that the threat of an attack was strong, with an estimated 150,000 or more Russian troops surrounding the country on three sides.

At the heart of the crisis are Russia’s demands that the West keep Ukraine and other former Soviet nations out of NATO, halt weapons deployments near Russian borders and roll back forces from Eastern Europe. The U.S. and its allies have roundly rejected those demands, but they offered to engage in talks with Russia on ways to bolster security in Europe.

Though Russia has said it is pulling back some troops, a senior U.S. administration official said some forces arrived only recently and that there had been a marked increase in false claims by Russians that the Kremlin might use as a pretext for an invasion. The official said those claims included reports of unmarked graves of civilians allegedly killed by Ukrainian forces, assertions that the U.S. and Ukraine are developing biological or chemical weapons, and claims that the West is funneling in guerrillas to kill Ukrainians.

The official was not authorized to speak publicly about sensitive operations and spoke to The Associated Press (AP) on condition of anonymity. The official did not provide underlying evidence for the assertions.

"We haven’t seen a pullback," U.S. Secretary of State Antony Blinken told ABC News, asserting that Russian President Vladimir Putin "can pull the trigger. He can pull it today. He can pull it tomorrow. He can pull it next week. The forces are there if he wants to renew aggression against Ukraine."

Asked why Russians would claim to be withdrawing when government intelligence, commercial satellite photos and social media videos showed no evidence of that, U.S. State Department spokesperson Ned Price said: "This is the Russian playbook, to paint a picture publicly ... while they do the opposite."

Maxar Technologies, a commercial satellite imagery company that has been monitoring the Russian buildup, reported that new photos show heightened Russian military activity near Ukraine, including the construction of a pontoon bridge in Belarus less than 6 kilometers (4 miles) from the Ukrainian border.

NATO Secretary-General Jens Stoltenberg said the alliance also had not seen "any withdrawal of Russian forces," as did some European governments. Ukrainian President Volodymyr Zelenskyy similarly dismissed the Russian claims.

"What is this? Rotations, withdrawal, returning back again," he said on a visit to the southeastern city of Mariupol. "It’s too early to rejoice."

The Ukrainian leader, who has repeatedly sought to project calm and strength during the crisis, declared Wednesday a day of "national unity" – a day that had been floated as a possibility for the start of an invasion.

"We are united by a desire to happily live in peace," Zelenskyy told the nation in an address. "We can defend our home only if we stay united."

Across the country, Ukrainians of all ages waved flags in the streets and from apartment windows.

Hundreds unfolded a 200-meter (650-foot) flag at Kyiv’s Olympic Stadium, while another was draped in the center of a shopping mall in the capital.

In the government-controlled part of Ukraine’s eastern region of Luhansk, where Russian-backed separatists have been fighting Ukrainian troops since 2014, residents stretched another huge flag across a street.

"This event, this number of people united around the Ukrainian flag will show that we stand for united Ukraine," resident Olena Tkachova said.

A 2015 deal brokered by France and Germany helped end the worst of the fighting in eastern Ukraine, but implementation has stalled. The deal, known as the Minsk agreement, would offer broad self-rule to the separatist territories and thus is resented by many in Ukraine.

A Ukrainian government official said in a television interview that Zelenskyy would consider holding a referendum on the Minsk agreement "if there are no other options or instruments." But Vice Prime Minister Iryna Vereshchuk said she was unaware that such an idea was under serious discussion.

The U.N. Security Council is scheduled to hold its annual meeting on the Minsk agreement on Thursday. Russia, which holds the rotating council presidency this month, will chair the meeting. At last year’s council meeting, Russia clashed with the U.S. and its Western allies over the conflict in eastern Ukraine and a similar, though likely broader, confrontation is expected this year.

Putin has signaled that he wants a peaceful path out of the crisis. His country has repeatedly complained that the U.S. and NATO have not responded satisfactorily in writing to its security concerns. Russian Foreign Ministry spokesperson Maria Zakharova said that Moscow is in the final phase of preparing its formal response to the West.

"After that, a schedule of further steps will be developed," she said on state television.

It appeared to be another indication that the Kremlin is determined to keep up the pressure for a while. Russian fighter jets flew training missions over neighboring Belarus, and paratroopers held shooting drills at firing ranges there as part of massive war games that the West feared could be used as cover for an invasion of Ukraine.

Ahead of a visit to Kyiv, British Foreign Secretary Liz Truss on Thursday said that Russia could drag out the Ukraine crisis for "months" in a challenge to Western unity. Truss warned of "severe economic costs for Russia" if it did invade, adding that it would make it "unconscionable" for its lucrative Nord Stream 2 gas pipeline to Europe to go ahead.

"There is currently no evidence the Russians are withdrawing from border regions near Ukraine," Truss wrote in the Daily Telegraph. She said Moscow "could drag this out much longer in a brazen ploy to spend weeks more – if not months – subverting Ukraine and challenging Western unity.

"We cannot allow this situation to become a running sore," she added, according to remarks carried by Reuters.

The head of British military intelligence said late Wednesday that "contrary to their claims, Russia continues to build up military capabilities near Ukraine.

"This includes sightings of additional armored vehicles, helicopters and a field hospital moving towards Ukraine's borders. Russia has the military mass in place to conduct an invasion of Ukraine," he said.

Foreign Minister Truss will leave London on Thursday to visit several European countries as part of diplomatic efforts to deter a Russian invasion of Ukraine. She will meet her Ukrainian and Polish counterparts during visits to both nations, before attending the Munich Security Conference in the southern German city on Saturday.

"Our friends such as Ukraine and Poland have lived in the constant shadow of such threatening behaviour for generations. That is why we must be unyielding in defense of self-determination and sovereignty," she wrote.

Russia is demanding a ban on Ukraine from entering NATO, but Truss said "we must preserve NATO's open-door policy and Ukraine's right to choose its own path."

British Defense Secretary Ben Wallace, speaking to Sky News, warned Putin that Moscow's aggressive military actions in 2014 resulted in more troops on its borders and more defense spending throughout NATO.

"That is the strategic error Putin is potentially about to make," he added.

Meanwhile, Russian Foreign Minister Sergey Lavrov said that Moscow will send a reply to the United States on the issue of security guarantees on Thursday, the TASS news agency reported. Moscow will make the letter public, Lavrov said.