RIGA, Latvia — NATO foreign ministers began talks here Tuesday as the alliance confronts mounting tensions with Russia over its military buildup near Ukraine.

U.S. Secretary of State Antony Blinken joined his counterparts from across the 30-member bloc as the Biden administration attempts to forge a unified transatlantic response to Russia’s deployment of troops and weaponry along its border with Ukraine, which officials in Kyiv and Washington say could indicate plans for a Russian invasion.

American officials have been considering measures they hope will deter Russian President Vladimir Putin from escalating Ukraine’s simmering conflict, including additional military aid to Kyiv or new sanctions on Russia. But they also hope to avoid provoking Moscow into further action as rhetoric grows more antagonistic on both sides.

Blinken, speaking alongside Latvian Foreign Minister Edgars Rinkevics ahead of the NATO ministerial, said steps to intensify the Ukrainian conflict would be a serious concern for the United States, as they would to smaller nations on Russia’s periphery, such as Latvia.

“Any renewed aggression would trigger serious consequences,” he said.

Blinken has sought to reinforce U.S. support for Europe following the unsettling effects of President Donald Trump’s skepticism about the alliance.

Asked by reporters whether the United States would stand up for allies, especially its less powerful ones, Blinken said the Biden administration was strongly committed to NATO’s mutual-defense pact and was working to invest in the alliance’s future.

“But ultimately, what I would say to you and say to anyone else is don’t judge us by what we say, judge us by what we do,” he said. “That’s the ultimate test.”

A possible renewed flash point over Ukraine, which is not a member of NATO, comes as the Biden administration hopes to shift its security focus from counterinsurgency to competition with China and Russia. On Monday, the Pentagon announced the conclusion of a months-long review of global troop placements, resulting in no major changes in Europe.

Blinken’s remarks came as Putin, in a potential shift, described the expansion of NATO military infrastructure into Ukraine as a “red line” for Russia. Previously, Russian officials said they considered NATO membership for Ukraine the red line.

Russian officials have taken a harder public line on Ukraine as U.S. and NATO officials raise alarms about the situation along the two countries’ border. Moscow has said the buildup is purely defensive.

Also on Tuesday, Russian Foreign Minister Sergei Lavrov told journalists that “if the West fails to keep Ukraine in check but instead chooses to stimulate it, we will definitely take all necessary steps to ensure our security.”

“Substantial forces and military hardware of NATO member states, including those American and British, are being deployed towards our border,” Lavrov added. “We simply have no right to rule out the chance of the Kyiv regime sliding into a reckless military venture.”

It is not yet clear whether Blinken will meet with Lavrov when the two men attend an Organization for Security and Cooperation in Europe meeting in Sweden later this week.

The crisis has further fanned tensions in Eastern Europe. On Monday, Belarus, a close Russia ally that for years took a neutral position on Ukraine, announced joint military drills with Russia on its southern border with Ukraine, accusing NATO of building up its offensive capabilities in the region.

President Alexander Lukashenko, whose government is already targeted by Western sanctions, said that “it is clear whose side Belarus will be on,” referring to Moscow, if war breaks out between Russia and Ukraine.

Also on the agenda for the NATO ministers is the migrant crisis along Belarus's border with Poland and the aftermath of the U.S. and NATO withdrawal from Afghanistan.

Blinken, asked about Ukrainian President Volodymyr Zelensky’s allegations about a failed coup plot by Russians and Ukrainians, pointed to what he called Russia‘s “playbook” but stopped short of confirming such a plan.

“Part of that playbook is to attempt to create and manufacture a so-called provocation as justification for something that Russia is planning to do all along,” he said. “Whether what’s been reported fits into that playbook, I don’t know.”

Isabelle Khurshudyan in Moscow contributed to this report.