Ukraine has urged NATO to prepare economic sanctions on Russia to deter a possible invasion by tens of thousands of Russian troops concentrated within reach of its border.

Ukraine's Foreign Minister Dmytro Kuleba said he would make the request to NATO foreign ministers meeting for the second day in Latvia to discuss how to respond to the Russian build-up and avert potentially the most dangerous crisis in relations with Moscow since the Cold War.

"We will call on the allies to join Ukraine in putting together a deterrence package," Kuleba told reporters as he arrived for the talks in Riga.

This should include preparing economic sanctions against Russia, in case it "decides to chose the worst-case scenario," Kuleba said, adding that NATO should also boost military and defence cooperation with Ukraine.

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Ukraine is not a member of NATO but the U.S.-led alliance has said it is committed to preserving the sovereignty of the country, which has tilted towards the West since 2014 and aspires to join both NATO and the European Union.

In response, Russia's President Vladimir Putin on Tuesday warned his country was ready with a newly tested hypersonic weapon in case NATO crossed its "red lines" and deployed missiles in Ukraine.

Putin said on Wednesday that Moscow wanted serious negotiations with the U.S. and its allies to extract legal guarantees that would rule out "any further NATO moves to the east and the deployment of weapons systems that threaten us in close proximity to Russian territory."

That is unlikely to be acceptable to the U.S., which has said no country has the right to veto Ukraine's NATO ambitions. U.S. Secretary of State Antony Blinken is due to meet Russia's Foreign Minister Sergei Lavrov in Stockholm on Thursday.

Moscow also backs separatists in a long-running war in the Donbass region of eastern Ukraine and accused Kyiv on Wednesday of mobilizing 125,000 troops, or half its army, in the conflict zone. Kyiv declined to comment.

The Kremlin said it feared Ukraine was gearing up to try to take back the rebel areas by force, something Kyiv denies, and accused it of "very dangerous adventurism."

It said Russia could not take any steps to de-escalate because of a large concentration of Ukrainian forces close to the border.

Ukraine's President Volodymyr Zelenskiy said direct talks with Moscow were needed to end the war in the east, which Kyiv says has killed more than 14,000 people.

"We must tell the truth, that we will not be able to stop the war without direct negotiations with Russia. And today this has already been recognized by all external partners," Zelenskiy told parliament.

Russia said it had started regular winter military drills in its southern military district, parts of which border Ukraine, and that 10,000 troops had relocated to training grounds across the huge area. Its ally Belarus has also announced joint military drills with Russia on the Ukraine border.

Meanwhile, Turkey's Foreign Minister Mevlut Cavusoglu said Ankara is in contact with Ukraine and Russia to ease tensions, adding that sanctions on Moscow will not solve the crisis.

Cover photo: Ukraine's President Volodymyr Zelenskiy addresses lawmakers during a parliamentary session in Kyiv, Ukraine December 1, 2021. /Reuters/Valentyn Ogirenko