MOSCOW — Russia warned today it would quickly take “retaliatory measures” if the U.S. and its allies reject its security demands and continue their “aggressive” policies, ratcheting up pressure on the West amid concerns that Moscow is planning to invade Ukraine.

Russia has repeatedly denied it has any such designs, but the United States and its NATO allies are worried because Russia has massed an estimated 100,000 troops near Ukraine’s border and launched a series of war games in the region.

At the heart of the standoff are questions about Ukraine’s future: Russia has demanded guarantees that NATO will never admit the country and other ex-Soviet nations as members and that the alliance will roll back troop deployments in other former Soviet bloc countries. Some of these, like the membership pledge, are nonstarters for NATO, creating a seemingly intractable stalemate that many fear can only end in a war.

Speaking to lawmakers today, Russian Foreign Minister Sergey Lavrov said he and other top officials will advise President Vladimir Putin on the next steps after receiving written replies from the United States to the demands. Those answers are expected this week — even though the U.S. and its allies have already made clear they will reject the top Russian demands.

“If the West continues its aggressive course, Moscow will take the necessary retaliatory measures,” he said.

While Russia is currently waiting for the American reply, Lavrov indicated it wouldn’t wait forever: “We won’t allow our proposals to be drowned in endless discussions,” he said.

Asked by lawmakers if Russia could expand military cooperation with Cuba, Venezuela and Nicaragua, Lavrov responded that Moscow has close ties with those countries. Earlier this month, Lavrov’s deputy pointedly refused to rule out the deployment of Russian military assets to Cuba and Venezuela — far closer to the U.S. than Ukraine — if Moscow’s security demands aren’t met.

NATO said this week it was bolstering its deterrence in the Baltic Sea region and the U.S. ordered 8,500 troops on higher alert for potential deployment to Europe. Western nations have also sent planeloads of weapons to help Ukraine strengthen its defenses.

Amid the escalating tensions, Ukrainian officials have sought to calm nerves.

Ukraine’s Foreign Minister Dmytro Kuleba said today that while the concentration of Russian troops near Ukraine poses a threat, “their number is now insufficient for a large-scale offensive.”

“They are still missing some key military elements and systems to mount a big, full-scale offensive,” Kuleba told reporters.

As others have, he noted that causing alarm could be an end in itself. Russia, he said, hopes to destabilize Ukraine by “spreading panic, raising pressure on Ukraine’s financial system and launching cyberattacks.”

“President Putin would be happy to see that plan succeed so that he doesn’t even need to turn to military force to put Ukraine in a vulnerable position,” he said.

His comments were latest from Ukrainian officials who have sought to reassure their citizens. Speaking late Tuesday in the second televised speech to the nation in as many days, President Volodymyr Zelenskyy said Ukraine was “strong enough to keep everything under control and derail any attempts at destabilization.”

Several rounds of high-stakes diplomacy have failed to yield any breakthroughs in the standoff, but another attempt was going forward today.

Presidential advisers from Russia, Ukraine, France and Germany are set to meet in Paris to discuss ways to revive a stalled peace agreement for eastern Ukraine.

In 2014, following the ouster of a Kremlin-friendly president in Kyiv, Moscow annexed Ukraine’s Crimean Peninsula and threw its weight behind a separatist insurgency in the country’s eastern industrial heartland. Fighting between Ukrainian forces and Russia-backed rebels has killed over 14,000 people, and efforts to reach a settlement have stalled.

Kremlin spokesman Dmitry Peskov said that Moscow expects a “good frank” talk at the Paris meeting.

In addition to the military moves, the U.S. and its allies have threatened sanctions like never before if Moscow sends its troops into Ukraine, but they have given few details, saying it’s best to keep Putin guessing.

On Tuesday, U.S. President Joe Biden told reporters that Putin “continues to build forces along Ukraine’s border,” and an attack “would be the largest invasion since World War II. It would change the world.” He warned that there would be serious economic consequences for Putin, including personal sanctions, in the event of an invasion.

Asked to comment on Biden’s statement, Peskov pointed out that the Russian president and other top officials don’t have assets in the West but reaffirmed that such U.S. sanctions would be “politically destructive” for bilateral ties.

Britain is also promising sanctions, and Foreign Secretary Liz Truss has urged European nations to do more to support Ukraine.

The U.K. has sent anti-tank weapons to Ukraine, though it has ruled out sending combat troops.

“We’ll be legislating to toughen up our sanctions regime and make sure we are fully able to hit both individuals and companies and banks in Russia in the event of an incursion,” she told the BBC. “What’s important is that all of our allies do the same.”

Amid the soaring tensions, the U.S., Britain, Australia, Germany and Canada have also moved to withdraw some of their diplomats and dependents from Kyiv.