BRUSSELS — Secretary of State Marco Rubio said Friday that Russia is running out of time to convince the Trump administration that it is serious about striking a peace deal with Ukraine and not just playing for time.

Speaking in Brussels after a two-day gathering of NATO ministers, Rubio said the United States was losing patience with “talks about talks” and hinted that Russia was in danger of facing more U.S. sanctions.

“We will know soon enough, in a matter of weeks, not months, whether Russia is serious about peace or not,” he told reporters. Members of Congress, he added, are already crafting new sanctions measures that administration officials are “not going to be able to stop” without signs of progress.

President Donald Trump has vowed to end the war in Ukraine and is mediating talks between Russia and Ukraine. Many observers had assumed that Russia would embrace such a deal and Ukraine would resist it, given that Russia occupies about one-fifth of its neighbor and has suffered staggering casualties.

But Rubio’s remarks were the latest sign that the Trump administration is coming around to a view held by the Biden administration and by Rubio himself when he was a Florida senator: that President Vladimir Putin of Russia does not bargain in good faith.

Many analysts say the Russian leader is stalling for time to press his military and political advantage.

Rubio spoke after a NATO gathering whose collegial photo-ops and press statements masked deep tensions between the U.S. and Europe over Ukraine, Trump’s market-rocking tariffs and even the fate of Greenland.

Rubio also conveyed Trump’s expectation that NATO members dramatically increase military spending to 5% of their gross domestic product — a tough pill for Europe to swallow as Trump’s tariffs threaten its economy.

In remarks to reporters, Rubio defended Trump’s tariffs as necessary but soft-pedaled the timeline for increased military spending as “a path of getting up to 5% at some point.” He said other NATO members were “open to doing more” to make the alliance stronger and less reliant on the United States.

A senior State Department official acknowledged that the tariffs had come up when Rubio met with his fellow ministers to discuss Ukraine. But the official, speaking on background to discuss private diplomacy, insisted that the mood in the room had been collegial.