U.S. President Donald Trump has paused all military aid to Ukraine following his clash with Ukrainian President Volodymyr Zelenskyy last week, a White House official said Monday.

"[The] president has been clear that he is focused on peace. We need our partners to be committed to that goal as well. We are pausing and reviewing our aid to ensure that it is contributing to a solution," said the official, speaking on the condition of anonymity.

Zelenskyy's office did not immediately respond to a Reuters request for comment outside office hours.

News of the pause was also reported by other major news agencies, including The Associated Press, BBC News and CBS News.

The move comes after Trump upended U.S. policy on Ukraine and Russia upon taking office in January, adopting a more conciliatory stance toward Moscow — and after an explosive confrontation with Zelenskyy at the White House on Friday in which Trump criticized him for being insufficiently grateful for the Washington's backing in the war with Russia.

Trump has also pressed for Ukraine to agree to give the U.S. access to its minerals, as a form of what Trump described as "equalization" for aid. So far, Ukraine has not signed any such arrangement.

Under former U.S. president Joe Biden, Washington had been a strong backer of Ukraine's fight against the Russian invasion.

WATCH | U.S. aid critical for Ukraine: Former PM:

Former Ukraine PM says it's 'very difficult' to win war without U.S.

Former Ukrainian prime minister Arseniy Yatsenyuk says President Volodymyr Zelenskyy has 'nothing to apologize for' after the U.S. president's White House confrontation, but says the 'free world' must 'do our utmost to have Americans back on track' if it hopes to win against dictators. 'We need them and they need us,' he said.

Biden was in office when Russia launched a full-scale invasion of Ukraine on Feb. 24, 2022. Ukraine and its neighbour have been locked in all-out war ever since.

The war has killed thousands of civilians in Ukraine and, Zelenskyy said last month, more than 45,000 of its soldiers.

But Ukraine has also brought the war to Russia, with long-range drone strikes and the capture of a slice of the Kursk region on the Russian side of the border.

Trump had previously claimed he could end the war in Ukraine within 24 hours. Yet six weeks into his presidency, the war still rages.