The UK was "intimately involved" in helping Ukraine and the US reach an agreement over a proposed ceasefire deal with Russia, according to UK government sources.

Ukrainian President Zelensky has said he is ready to accept an immediate 30-day ceasefire but that it is up to the US to convince Russia to agree, after talks in Saudi Arabia.

The BBC has been told that over the past week there has been a concerted European effort, led by Sir Keir Starmer, to get the US and Ukraine back in good favour with one another.

Sir Keir praised the "remarkable breakthrough" and called it an "important moment for peace in Ukraine".

Following the announcement, the Trump administration said it would reinstate military aid to Ukraine and restart intelligence-sharing with Kyiv - after abruptly halting this after Donald Trump and Zelensky's row in the Oval Office.

The UK sources say that last week the prime minister's National Security Adviser, Jonathan Powell, worked with his US counterpart Mike Waltz, and German and French officials, to fashion a plan for a ceasefire and the steps that might follow.

Over the weekend Powell travelled to Kyiv to meet Zelensky and help draft a written proposal which included a temporary pause in fighting, then confidence-building measures such as an exchange of prisoners-of-war, the return of Ukrainian children taken by Russia and the release of civilians.

That proposal was agreed by the Ukrainians and the Americans, setting the stage for what happened in Saudi Arabia on Tuesday.

Following the talks between White House and Ukrainian officials in Saudi Arabia, Sir Keir congratulated the two men on the agreement, adding "we now all need to redouble our efforts" to secure a peace deal for Ukraine.

He said: "As both American and Ukrainian delegations have said, the ball is now in the Russian court. Russia must now agree to a ceasefire and an end to the fighting too."

Trump told reporters that US officials would discuss the deal with Moscow either late on Tuesday or Wednesday as he wanted to "get this show on the road".

When asked about the 30-day ceasefire proposal, Kremlin spokesman Dmitry Peskov said "let's not get ahead of ourselves".

Speaking at a daily press briefing, he said Russia was "carefully studying the statements made after the meeting" and that the Kremlin needed to be briefed by the US on the outcome of US-Ukrainian talks in Saudi Arabia before commenting on whether a proposed ceasefire was acceptable to Russia.

Peskov did not rule out the need for a phone conversation between Vladimir Putin and Trump.

Labour MP Dame Emily Thornberry, who chairs the Foreign Affairs Select Committee, said Britain has played a "big part" in where things currently stand in the war in Ukraine, including proposals for a halt in fighting.

"I think we need to just pause this moment and appreciate the calm and optimism and hope," she told the BBC's Today programme.

"We might have peace in Ukraine, this is a step along that road, it could happen and I think we need to at this stage kind of appreciate what it is that we have achieved and I think that Britain has played a big part in that."

She also said that Powell had "earnt his money", noting that the work he has done in helping Ukraine and the US reach an agreement over a proposed ceasefire deal with Russia is an "achievement".

On Saturday, Sir Keir will host a phone call of leaders which he has dubbed the "coalition of the willing" to discuss peacekeeping efforts aimed at deterring Russian President Putin from launching future incursions into Ukraine.

Those joining the call are "ready to help bring an end to this war in a just and permanent way that allows Ukraine to enjoy its freedom", he said.

One aim of the European teams working behind the scenes has been to ensure that it is now Russia that is in the spotlight: does it want peace?

A UK source said "the ball is firmly in the Russian court. Will they reciprocate and stop the fighting to allow serious negotiations on a lasting peace or will they continue to slaughter innocent civilians?".

Hundreds of thousands of people, most of them soldiers, are believed to have been killed or injured on both sides, and millions of Ukrainian civilians have fled as refugees, since Russia invaded Ukraine just over three years ago.

Russia's attacks on Ukraine have continued with Ukrainian authorities confirming one missile attack in President Zelensky's hometown of Kryvyi Rih - which killed one person - and an attack on a cargo ship in the port city of Odessa - which killed four Syrian nationals and damaged port infrastructure and grain storage facilities.