US Secretary of State Marco Rubio said Tuesday Washington will cease mediating Russia-Ukraine peace talks unless concrete progress is proposed. Frustrated by stalled negotiations and ongoing violence since Russia’s 2022 invasion, he warned of disengagement without viable solutions. 

Secretary of State Marco Rubio warned Tuesday that the United States would end mediation unless Russia and Ukraine put forward "concrete proposals", as US patience wanes on an early priority for Donald Trump.

The US president had vowed to end the war in his first 24 hours back in the White House but, as Trump celebrates 100 days in office, Rubio has suggested the administration could soon turn attention to other issues.

"We are now at a time where concrete proposals need to be delivered by the two parties on how to end this conflict," State Department spokeswoman Tammy Bruce told reporters, in what she said was a message from Rubio.

"If there is not progress, we will step back as mediators in this process."

She said it would ultimately be up to Trump to decide whether to move ahead on diplomacy.

Russian President Vladimir Putin recently proposed a three-day ceasefire around Moscow's commemorations next week for the 80th anniversary of the end of World War II.

But Putin has rebuffed a Ukrainian-backed US call for a 30-day ceasefire.

The United States wants "not a three-day moment so you can celebrate something else – a complete, durable ceasefire and an end to the conflict", Bruce said.