Secretary of State Marco Rubio warned Tuesday that the United States would give up on 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.

Means of pressure

It remains unclear if Rubio is actually ready to turn the page or is seeking to pressure the two countries.

The United States already put together a framework proposal which Ukrainians feel bows to Russian demands.

Trump has suggested an official recognition of Russia's takeover in 2014 of Crimea, an annexation rejected by nearly all the world, in addition to land swaps.

"We all want this war to end in a fair way — with no rewards for Putin, especially no land," Ukrainian President Volodymyr Zelensky told an event in Poland by videoconference on Tuesday.

Russia has also not moved on the proposal with many experts believing Moscow now sees an upper hand — on the battlefield and diplomatically, with Trump eager to reconcile.

Russia's ambassador to the United Nations, Vassily Nebenzia, sought to blame Zelensky and said that Russia would keep speaking with the United States.

Zelensky "is bent on escalating the conflict. He's recklessly rejecting the United States' balanced peace proposals," Nebenzia told a UN Security Council meeting.

US diplomat John Kelley told the session that both sides would benefit from working off the US framework and condemned Russian strikes into Ukraine.

"Right now, Russia has a great opportunity to achieve a durable peace," Kelley said.

Trump, criticizing his predecessor Joe Biden for shunning Putin over the February 2022 invasion, reached out by telephone to the Russian leader and has sent his business friend turned globe-trotting ambassador Steve Witkoff to see him.

Trump in turn berated Zelensky in a February 28 White House meeting, with Trump and Vice President JD Vance accusing the wartime leader of ingratitude for US weapons under Biden.

Ukraine quickly tried to make amends by backing US diplomatic efforts and pursuing a deal in which the United States would control much of the country's mineral wealth.

'Fatally mismanaged' talks

US Senator Jeanne Shaheen, the top Democrat on the Senate Foreign Relations Committee, said Tuesday that recognizing "Russia's illegal annexation of Crimea would invite additional aggression from Moscow and Beijing."

"I have endeavored to give President Trump the space to negotiate a just and lasting peace in Ukraine, which is a goal we both share," she said.

"However, President Trump and his team have fatally mismanaged these negotiations — offering concession after concession to Russia, throwing away our leverage and fracturing the united front with our allies that is critical to ending this war," she said.

Ukraine on Tuesday ordered the evacuation of seven villages in the eastern Dnipropetrovsk region which used to be remote from the frontlines but are now under threat as Russian forces close in.

Last week a ballistic missile ripped into a residential area of Kyiv in one of the deadliest attacks on the capital since the invasion.

Trump, who has claimed that Putin would not have attacked Ukraine if he were in power in 2022, wrote, "Vladimir, STOP," on social media after the attack.