Russian President Vladimir Putin has agreed to pause attacks on Ukrainian energy infrastructure while negotiations for a permanent ceasefire take place, the White House and the Kremlin say.
But Russia has indicated it will only agree to a full ceasefire if Ukraine's allies, including the US, stop providing arms and sharing intelligence with Kyiv.
The agreement follows a phone call between US President Donald Trump and Mr Putin lasting at least 90 minutes on Tuesday, local time.
It falls short of the immediate 30-day ceasefire proposed by the US, and agreed to by Ukraine, after talks in Saudi Arabia last week.
But Mr Trump said the leaders reached "an understanding that we will be working quickly to have a complete ceasefire and, ultimately, an end to this very horrible war between Russia and Ukraine".
An official White House statement, released shortly after the call, said:
"The leaders agreed that the movement to peace will begin with an energy and infrastructure ceasefire, as well as technical negotiations on implementation of a maritime ceasefire in the Black Sea, full ceasefire and permanent peace.
"These negotiations will begin immediately in the Middle East."
A translated statement from Russia's foreign ministry said the two leaders had a "detailed and frank" exchange of views.
It said Mr Putin "responded positively" to Mr Trump's proposal for a halt on attacks on energy infrastructure, and "immediately gave the Russian military the corresponding order".
However, Mr Putin raised "a number of significant points" in response to his plan for a wider, 30-day ceasefire, the statement said.
"It was emphasised that the key condition for preventing the escalation of the conflict and working towards its resolution through political and diplomatic means should be the complete cessation of foreign military aid and the provision of intelligence information to [Kyiv]."
Mr Trump later said Putin did not talk to him about ending aid.
"We talked about a lot of things, but aid was never discussed," he told Fox News.
Ukrainian President Volodymyr Zelenskyy said Ukraine would support the proposal, and that he hoped to speak to Mr Trump soon.
"I think it will be right that we will have a conversation with President Trump and we will know in detail what the Russians offered the Americans or what the Americans offered the Russians," Mr Zelenskyy said, according to a translation by news agency Reuters.
He also said he hoped Ukraine's partners would not cut military aid for Ukraine, as Mr Putin has demanded.
Earlier this month, Mr Zelenskyy had agreed to the American proposal for a 30-day ceasefire after the US put him under intense pressure by halting intelligence and aid to Ukraine and threatening to pull military support completely.
After the details of the phone call were made public, French President Emmanuel Macron and German Chancellor Olaf Scholz released statements saying no ceasefire could be achieved without talks involving Ukraine.
In its statement, the Russian foreign ministry said a prisoner exchange would take place on Wednesday, with both Russia and Ukraine to release 175 detainees.
It also said another 23 seriously injured Ukrainian soldiers would be transferred from Russian medical facilities.
Both countries' statements expressed a desire to improve bilateral relations.
The White House said this could include "enormous economic deals" once peace had been achieved.
The Russian statement said Mr Trump supported a suggestion put forward by Mr Putin to organise ice hockey matches involving players from the two countries' national leagues.
