Ukraine urged NATO on Wednesday to prepare economic sanctions to impose on Russia and requested increased military cooperation as the country joined the Western alliance for talks on how to deter Russia from a renewed attack after it amassed troops close by.

Ukraine, a former Soviet republic that now aspires to join the European Union and NATO, has become a potential flashpoint between Russia and the West as relations have soured to their worst level in the three decades since the Cold War ended.

"We will call on the allies to join Ukraine in putting together a deterrence package," Ukraine's Foreign Minister Dmytro Kuleba told reporters as he arrived for talks with his NATO counterparts in the Latvian capital Riga. As part of this package, NATO should prepare economic sanctions against Russia in case it "decides to choose the worst-case scenario," he said, adding that the alliance should also boost military and defense cooperation with Ukraine.

"We are confident that if we join efforts, if we act in a coordinated fashion, we will be able to deter President Putin and to demotivate him from choosing the worst-case scenario, which is a military operation," Kuleba said.

NATO Secretary-General Jens Stoltenberg told reporters Tuesday that the United States-led military organization must prepare for the worst as concern mounts that Russia could be preparing to invade Ukraine. NATO is worried about a Russian buildup of heavy equipment and troops near Ukraine’s northern border, not far from Belarus. Ukraine says Moscow kept about 90,000 troops in the area following massive war games in western Russia earlier this year, and could easily mobilize them.

"Any future Russian aggression against Ukraine would come at a high price and have serious political and economic consequences for Russia," Stoltenberg told reporters after the first day of talks between the 30 allies in Riga.

Ukrainian President Volodymyr Zelenskyy said last week that his country’s intelligence service had uncovered plans for a Russia-backed coup. Russia denied the allegation and rejected the assertion that it is planning to invade Ukraine.

"We must acknowledge the truth that we cannot end the war without direct negotiations with Russia," Zelenskyy said in his annual state of the nation address in parliament on Wednesday. All foreign partners had already admitted this, he said.

He also used the occasion to laud the Ukrainian army, saying, "We know that our army is the best in the world and defends us" – to applause from lawmakers.

Danish Foreign Minister Jeppe Kofod told reporters upon arrival for the NATO session that any military operation that would violate the sovereignty of Ukraine would be met with "severe consequences" and that Denmark was ready to engage with "heavy" sanctions. His comments echoed those of NATO and the U.S., who on Tuesday issued stark warnings to Russia that it would pay a high price for any new military aggression against Ukraine.

Acting German Foreign Minister Heiko Maas said that Moscow would have to "pay a high price for any form of aggression," while British Foreign Secretary Liz Truss warned Moscow that "an incursion into Ukraine would be a strategic mistake."

It is still unclear how NATO states would respond if Moscow were to send troops over the border, and whether Russia would indeed risk such an escalation. Western countries already sanctioned Russia over the Ukraine conflict. Harsher punitive measures would be expected, but a military response is deemed unlikely. The alliance supports the Ukrainian army with training and equipment.

Russian President Vladimir Putin countered that Russia would be forced to act if U.S.-led NATO placed missiles in Ukraine that could strike Moscow within minutes. U.S. Secretary of State Antony Blinken said he would have more to say on the issue on Wednesday after consulting with NATO allies. Blinken is scheduled to give a news conference at 1:45 p.m. GMT.

Putin said Tuesday that military exercises and other moves by the West and Ukraine threaten Russia's security, warning against crossing the Kremlin's "red lines."

"Look, they spoke about a possible Russian military intervention in Ukraine at the beginning of the year. But as you see this did not happen," Putin said.

Moscow said Wednesday that Ukraine has massed tens of thousands of troops in the country's east, where Kyiv is fighting pro-Russian separatists.

"The Armed Forces of Ukraine are building up their military strength, massing heavy equipment and personnel," Russian Foreign Ministry spokesperson Maria Zakharova told reporters. "According to some reports, the number of Ukrainian troops in the conflict zone has already reached 125,000 personnel," she claimed and said that this represented half of Kyiv's troops.

The comments followed the Ukrainian Foreign Ministry saying Tuesday that Russia had massed 115,000 troops around Ukraine on the Crimean Peninsula – which Moscow annexed in 2014 – and in two eastern regions occupied by the breakaway fighters. Kyiv and its Western allies have long accused Russia of sending troops and arms to support the separatists – claims Moscow denies – who seized the territory shortly after Russia annexed Crimea.

The conflict, which has claimed more than 14,000 lives, escalated at the beginning of the year. While Moscow later announced a drawback, Ukraine and its ally the U.S. said at the time that the withdrawal was limited. Washington has routinely in recent weeks warned that Russia could cite a trumped-up provocation by Ukraine as an excuse to launch an assault, an allegation the Kremlin has denounced as hysteria.

Meanwhile, Belarusian President Alexander Lukashenko has recognized the annexed Ukrainian Black Sea peninsula of Crimea as Russian for the first time after a long period of hesitation. "Crimea is ... de facto a Russian Crimea," Lukashenko said in an interview with the Russian state agency Ria Novosti, excerpts of which were published on Wednesday. "After the referendum, Crimea also became Russian by right," the 67-year-old said, referring to a controversial referendum in 2014 after which Russia annexed Crimea against international protest.

While Russia's Foreign Minister Sergei Lavrov stressed that "nothing has to be done and no laws have to be passed" for recognition, Kuleba said that "the potential recognition of the occupied Crimea by Belarus will be a point of no return in our bilateral relations, and we will act respectively."

"Because for us, Crimea is not a field for compromises," Kuleba said.