RIGA, Latvia—NATO foreign ministers are meeting here Tuesday to calibrate a response to Russia’s military buildup around Ukraine, seeking to deter the Kremlin from any potential assault while making clear the limits of its support.

Concern over the Russian buildup has risen in recent weeks. The U.S. has briefed allies that Moscow could launch a new military operation in Ukraine, following its seizing of Crimea and covert invasion of its neighbor’s east in 2014. Russia, which wants to draw the former Soviet republic back into...

RIGA, Latvia—NATO foreign ministers are meeting here Tuesday to calibrate a response to Russia’s military buildup around Ukraine, seeking to deter the Kremlin from any potential assault while making clear the limits of its support.

Concern over the Russian buildup has risen in recent weeks. The U.S. has briefed allies that Moscow could launch a new military operation in Ukraine, following its seizing of Crimea and covert invasion of its neighbor’s east in 2014. Russia, which wants to draw the former Soviet republic back into its orbit, says it has no plans to invade and can move troops as it wishes on its sovereign territory.

The U.S. and allies have warned that an invasion would spark a sharp response, pointing to earlier financial, political and other sanctions, arms deliveries to Ukraine and the positioning of new North Atlantic Treaty Organization forces in the alliance’s east.

But allies have also said they have no obligation to defend Ukraine, which as a partner of NATO, but not a member, isn’t covered by the alliance’s mutual defense pact.

NATO’s deliberations over a response underscores its dilemma over Ukraine, which it promised membership in 2008 without setting a timetable. The West has plowed billions of dollars of financial and military support into Ukraine since 2014, but stopped short of offering a clear path to NATO membership.

Secretary of State Antony Blinken arrived in Riga late Monday and met with Latvian leaders ahead of the start of NATO consultations.

“Any escalatory actions by Russia would be a great concern to the United States,” Mr. Blinken said at a press conference with Latvian Foreign Minister Edgars Rinkevics. “Any renewed aggression would trigger serious consequences,” Mr. Blinken said, declining to elaborate but saying he would have more to say Wednesday after consulting with other NATO allies.

“We will be consulting closely with NATO allies and partners in the days ahead, particularly in the context of concerns raised by Russia’s actions along borders, about whether there are other steps that we should take as an alliance to strengthen our defense, to strengthen our resilience, to strengthen our capacity.”

NATO Secretary-General Jens Stoltenberg said Russia had amassed tens of thousands of combat-ready troops around Ukraine and in Crimea, including armored units, drones and electronic-warfare systems. In an interview with a small group of reporters Monday, he said Russia’s intentions were unclear, and that he expected alliance foreign ministers to send a clear message to Russia that it should take steps to reduce tensions.

The Riga meeting is aimed at working toward a response to Russia’s military buildup around Ukraine.

Photo: gatis rozenfelds/latvia's state/Shutterstock

“If they decide once again to use military force against a sovereign nation, Ukraine, then there will be a price to pay,” Mr. Stoltenberg said.

Ukraine wants NATO to make good on the promise of membership, but President Biden has said the country needs to do more to fight corruption. Privately, officials from allied countries say Ukraine won’t be offered membership soon.

Russian President Vladimir Putin has stepped up complaints about Western deliveries of weapons to Ukraine, flights by warplanes near Russia and military exercises in the Black Sea. Mr. Putin told foreign ministry officials on Nov. 18 that the West had paid insufficient heed to Russia’s warnings of “red lines” in what he described as NATO’s eastward military expansion.

Some European countries such as Germany are wary of provoking Russia. Others say that Western hesitation over stronger support for Ukraine encourages Russia to push further.

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“Russians know what they want,” Latvian Defense Minister

Artis Pabriks said in an interview, “but the problem with our own thinking is that we don’t decide what we want and what we will do, and once we hesitate, the Russians win.”

NATO countries, particularly from Europe, should offer more military assistance to Ukraine, he said, and bolster their own military forces in the alliance’s east, he said. Latvia and its neighbors have called for a permanent U.S. military presence to deter Russia.

NATO set up four multinational battle groups with a total of some 5,000 troops in Latvia, Lithuania, Estonia and Poland. Military analysts see the Baltic region as a weak point for NATO given Russia’s overwhelming military strength, which it could use before allied reinforcements could arrive.

Latvia last week launched an annual live-fire military exercise called Winter Shield to test the readiness of alliance forces, including from the U.S., to conduct a defensive operation.

On Monday, armored vehicles from Latvia and Spain practiced disrupting the advance of a hypothetical attacker advancing toward Riga.

Allied forces are training how to disrupt, delay and block the enemy, said Latvian Army Maj. Guntis Taurins. “And finally, with a counterattack, we will destroy the adversary,” he said.

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Write to James Marson at james.marson@wsj.com