The US leader has switched Washington's focus from backing Kyiv's fight against Russia's invasion to trying to negotiate a peace deal with President Vladimir Putin to halt the war.

Britain and Germany took the reins of a meeting of Ukraine's backers at NATO's headquarters in Brussels -- that used to be chaired by the United States under president Joe Biden.

US Defense Secretary Pete Hegseth dialled into the talks via video call.

"In the weeks to come, we will see what's going to happen with the US participation, with the US support. I am not able to have a look in the crystal ball," German defence minister Boris Pistorius said.

"We take on more responsibility as Europeans."

British defence minister John Healey said overall some 21 billion euros ($24 billion) more has been promised towards helping arm Ukraine.

He said London was looking to surge support worth $450 million -- including thousands of drones -- to Kyiv's fighters on the front line.

"2025 is the critical year for this war in Ukraine, and now is the critical moment in that war," Healey said.

"We are sending a signal to Putin, but we are also sending a message to Ukraine, and we are saying to Ukraine, we stand with you in the fight."

Ukraine's defence minister, Rustem Umerov, said that "Europe is taking over the lead in security assistance, for which we are thankful".

"It's a share of responsibilities, European partners are taking the lead and the US is beside us and focused on the peace."