U.S. President Donald Trump set a new deadline on Monday of 10 or 12 days for Russia to make progress toward ending the war in Ukraine or face consequences, underscoring frustration with Russian President Vladimir Putin over the 3-1/2-year-old conflict.

Trump has threatened sanctions on both Russia and buyers of its exports unless progress is made. The fresh deadline suggests the U.S. president is prepared to move forward on those threats after previous hesitation to do so.

Speaking in Scotland, where he was holding meetings with European leaders and playing golf, Trump said he was disappointed in Putin and shortening a 50-day deadline he had set on the issue earlier this month.

"I'm going to make a new deadline of about ... 10 or 12 days from today," Trump told reporters during a meeting with British Prime Minister Keir Starmer. "There's no reason in waiting... We just don't see any progress being made."

There was no immediate comment from the Kremlin.

In a post on X, former Russian President Dmitry Medvedev, a close ally of Putin, said Trump was playing "a game of ultimatums" that could lead to a war involving the U.S.

Medvedev wrote: "Each new ultimatum is a threat and a step towards war. Not between Russia and Ukraine, but with (Trump's) own country."

Ukrainian President Volodymyr Zelenskiy praised Trump's "particularly significant" statement as timely in trying to move forward to a peace settlement.

"Clear stance and expressed determination by @POTUS – right on time, when a lot can change through strength for real peace," Zelenskiy wrote on X.

"I thank President Trump for his focus on saving lives and stopping this horrible war," Zelenskiy said.

Ukraine, he said later in his nightly video address, favoured tougher sanctions as a "key element" in ending the war.

"Russia pays attention to sanctions, pays attention to such losses," he said

Trump, who has expressed annoyance also with Zelenskiy, has not always followed tough talk about Putin with action, citing what he deems a good relationship that the two men have had previously.

On Monday, Trump indicated he was not interested in more talks with Putin. He said sanctions and tariffs would be used as penalties for Moscow if it did not meet Trump's demands.

"There's no reason to wait. If you know what the answer is going to be, why wait? And it would be sanctions and maybe tariffs, secondary tariffs," Trump said. "I don't want to do that to Russia. I love the Russian people."

Ukraine had proposed a summit between Putin and Zelenskiy before the end of August, but the Kremlin has said that timeline was unlikely and that a meeting could only happen as a final step to clinch peace.

Russia's foreign ministry said on Saturday that if the West wanted real peace with Ukraine, it would stop supplying Kyiv with weapons.

Trump has repeatedly voiced exasperation with Putin for pursuing attacks on Ukraine despite U.S. efforts to end the war. Trump has played up successes in other parts of the world where the United States has helped to broker peace agreements and has been flattered by some leaders who suggest he should be given the Nobel Peace Prize.

"I'm disappointed in President Putin," Trump said on Monday. "I'm going to reduce that 50 days that I gave him to a lesser number because I think I already know the answer what's going to happen."

Trump, who is also struggling to achieve a peace deal in Gaza, has touted his role in ending conflicts between India and Pakistan as well as Rwanda and Congo. Before returning to the White House in January, Trump campaigned on a promise to end Russia's conflict with Ukraine in a day.

"We thought we had that settled numerous times, and then President Putin goes out and starts launching rockets into some city like Kyiv and kills a lot of people in a nursing home or whatever," Trump said. "And I say that's not the way to do it."