Rishi Sunak said the UK would “support our allies” as Joe Biden pledged US support for Poland but stated it was “unlikely” Russia fired a missile that killed two people in the eastern European country.

The president’s assessment was later backed up preliminary assessments from US intelligence suggesting the missile was fired by Ukrainian forces at an incoming Russian one.

The Prime Minister joined an emergency morning meeting on the incident at the G20 summit in Bali.

He was pictured sitting next to the US President, who called the roundtable of likeminded G7 and Nato leaders.

French President Emmanuel Macron, German Chancellor Olaf Scholz, Japan’s premier Fumio Kishida, Canada’s Justin Trudeau, Italian PM Giorgia Meloni, Ursula von der Leyen and Charles Michel from the European Commission and European Council, respectively, Spanish PM Pedro Sanchez and Dutch PM Mark Rutte were also gathered in the room.

In an official read-out of the meeting, issued by the European Union, the leaders said they agreed to offer their “full support for and assistance with Poland’s ongoing investigation”, while reaffirming their “steadfast support for Ukraine and the Ukrainian people in the face of ongoing Russian aggression”.

It comes as Mr Biden held a call with Polish President Andrzej Duda, in which the American “offered full US support for and assistance with Poland’s investigation”.

The Prime Minister, who is currently at the G20 in Bali with other world leaders, said he had spoken to Foreign Secretary James Cleverly and Defence Secretary Ben Wallace about the incident.

Mr Sunak also spoke himself to Mr Duda and “reiterated the UK’s solidarity” with the country and “expressed condolences for the victims and their families”.

He tweeted: “We are urgently looking into reports of a missile strike in Poland and will support our allies as they establish what has happened.

“We are also coordinating with our international partners, including NATO.”

According to Downing Street, Mr Sunak offered Poland “any assistance needed to urgently establish what happened”.

“The leaders agreed to remain in close contact and continue co-ordinating with our international partners, including Nato allies, on the next steps,” a spokesperson said.

Mr Cleverly earlier said that the UK was “urgently looking” into the reports.

Little information is so far known about the incident, but it has already sparked concern in Ukraine and among the war-torn nation’s allies in Europe and beyond.

The Polish Foreign Ministry late on Tuesday said that a Russian-made missile fell in eastern Poland and killed two people.

The ministry said foreign minister Zbigniew Rau summoned the Russian ambassador and “demanded immediate detailed explanations”.

Mr Biden, in his call with the Polish president, “offered full US support for and assistance with Poland’s investigation” and “reaffirmed the United States’ ironclad commitment to Nato”.

Mr Biden also spoke to Nato secretary general Jens Stoltenberg, who was among those to hold a call with Mr Duda.

Mr Stoltenberg said Nato was “monitoring the situation”, tweeting: “Allies are closely consulting. Important that all facts are established.”

It came as Ukrainian President Volodymyr Zelensky decried the missile strike as “a very significant escalation” of his country’s war with Russia.

In his nightly address, the Ukrainian leader said the reported strikes offered proof that “terror is not limited by our state borders”.

“We need to put the terrorist in its place. The longer Russia feels impunity, the more threats there will be for everyone within the reach of Russian missiles,” Mr Zelensky said.

European leaders were among those expressing deep concern about the development, amid urgent efforts to determine the exact circumstances behind the incident.

European Commission president Ursula von der Leyen was among those registering her alarm.

She tweeted: “Alarmed by reports of an explosion in Poland, following a massive Russian missile strike on Ukrainian cities.

“I extend my condolences and my strongest message of support and solidarity with Poland and our Ukrainian friends.”