US President Donald Trump has paused military aid to Ukraine following his clash with Ukrainian President Volodymyr Zelensky last week, a White House official said, deepening the fissure that has opened between the two one-time allies.

The move comes after Trump upended US policy on Ukraine and Russia upon taking office in January, adopting a more conciliatory stance towards Moscow - and after an explosive confrontation with Zelensky at the White House on Friday in which Trump criticiSed him for being insufficiently grateful for Washington's support.

"President Trump 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 a White House official.

The White House had no immediate comment on the scope and amount of aid affected or how long the pause would last.

The Pentagon could not provide further details.

Zelensky's office did not immediately respond to a Reuters request for comment nor did the Ukrainian Embassy in Washington.

On Monday, Trump again said Zelensky should be more appreciative of American support after earlier responding angrily to an Associated Press report quoting Zelensky as saying the end of the war is "very, very far away."

"This is the worst statement that could have been made by Zelensky, and America will not put up with it for much longer!" Trump wrote on Truth Social. (Reuters)