Poland and Lithuania joined Ukraine on Monday to call for stronger Western sanctions against Moscow amid a Russian troop buildup near the Ukrainian border that has fueled fears of an invasion.

U.S. intelligence officials say Russia has amassed 70,000 troops near its border with Ukraine and is preparing for a possible invasion early next year. Moscow has denied an intention to attack, but demanded that NATO deny membership to Ukraine and other former Soviet countries and roll back the alliance’s military deployments in Central and Eastern Europe.

Polish President Andrzej Duda and Lithuanian President Gitanas Nauseda met with Ukrainian President Volodymyr Zelenskyy in Huta in western Ukraine’s Carpathian Mountains in a show of support in the face of a Russian troop buildup.

In a joint statement issued after the meeting, the three leaders “called upon the international community to step up sanctions on the Russian Federation over its ongoing aggression against Ukraine and once again urged the Kremlin to de-escalate the situation by withdrawing its troops from the Ukrainian borders and temporarily occupied territories.”

Russia annexed Ukraine’s Crimean Peninsula in 2014 and shortly after cast its support behind a separatist rebellion in the country’s east. More than seven years of fighting has killed over 14,000 people and devastated Ukraine’s industrial heartland, known as the Donbas.

“Our common task is to deter the threat posed by Russia and defend Europe from Russia’s aggressive policies,” Zelenskyy said at a news conference after the talks. “Ukraine, Poland and Lithuania are the vanguard of that deterrence today.”

The Ukrainian leader called for “powerful preventative actions, powerful serious sanctions to exclude any thought about escalation.”

Nauseda emphasized that any attempts by Russia to draw “red lines” are “unacceptable in Europe in the 21st century.”

Duda also warned strongly against any appeasement of Moscow.

“I’m categorically against making any concessions to Russia,” Duda said. “It’s clear that it’s Russia which must step back.”

Moscow on Friday published draft security documents demanding that the U.S. and its NATO deny membership to Ukraine and other former Soviet countries and roll back the alliance’s military deployments in Central and Eastern Europe — bold ultimatums that are almost certain to be rejected by the U.S. and its allies.

Russian President Vladimir Putin raised the demand for security guarantees in last week’s video call with U.S. President Joe Biden who warned that Russia would face “severe consequences” if Moscow attacked its neighbor.

Russian diplomats have said that Moscow will have to up the ante if its demands are rejected.

Russian Deputy Foreign Minister Alexander Grushko warned that Moscow will respond in kind if NATO deploys missiles capable of reaching Russia in a few minutes.

“If offensive weapons capable of reaching our control centers appear on the territory of NATO members, we will have to create a similar situation for our counterparts,” Grushko told the daily Rossiyskaya Gazeta.

(AP)