President Trump on Tuesday unleashed weeks of frustration with President Vladimir V. Putin of Russia over what he described as “meaningless” gestures toward peace, a day after Mr. Trump said the United States would resume sending munitions to help Ukraine fend off Russia’s multiyear invasion.

The remarks from Mr. Trump were his harshest toward Mr. Putin since he was first elected president in 2016, and came as an abrupt change in public posture toward the Russian leader after months of failing to forge peace in a conflict he once boasted he could resolve in a day.

“We get a lot of bullshit thrown at us by Putin, if you want to know the truth,” Mr. Trump told reporters during a cabinet meeting at the White House. “He’s very nice to us all the time, but it turns out to be meaningless.”

The president’s disenchantment with his Russian counterpart, along with more positive recent interactions he has had with President Volodymyr Zelensky of Ukraine, appeared to have driven his decision to resume sending some air defense interceptors and precision-guided bombs and missiles to Ukraine after their delivery had been halted last month.

At the time, administration officials said that the pause was necessary to assess whether the Pentagon’s weapons stockpiles were dwindling too low. Officials have not said who directed the pause.

It is unclear how quickly the initial tranche of paused weapons, which was held up in Poland, will arrive in Ukraine. But the decision to release the munitions was cheered in Ukraine, which suffered a major Russian air attack on Kyiv and other cities late last week, shortly after a phone call between Mr. Trump and Mr. Putin.