German Chancellor Olaf Scholz on Wednesday urged European nations to step up weapons pledges to Ukraine, raising the spectre that help from biggest contributor United States could fall away.

"Europe must do more to support Ukraine in the defence of its own country," Scholz told Die Zeit weekly in an interview.

"The contributions that European nations have earmarked for 2024 so far are not big enough," he added, urging them to discuss how each country can "significantly expand the support" to Kyiv.

The chancellor also said he is "rather irritated" that Germany is constantly being criticised for not doing enough, when it is already "doing more than all other EU nations, much much more".

Ukraine has been pleading for more ammunition and armaments in its fight against Russian troops. Among the weapons Kyiv is seeking are Taurus cruise missiles which Germany has so far declined to provide.

Nevertheless, Germany makes up more than half of Europe's known weapon deliveries to Ukraine, and Scholz said it would be "hubris to think that we can do this alone in the long term".

"It would not be good news if Germany, should the US drop off as a supporter, were to become the biggest supporter of Ukraine at the end," he said, adding that "we are, as (former chancellor) Helmut Schmidt once said, only a medium-sized power".

President Joe Biden has made backing Ukraine a priority and US weapons and financial assistance have been crucial in helping the pro-Western country battle against a far larger attacking Russian force.

But opposition Republicans have led a push to halt the effort, refusing to authorise new budget outlays unless the Democrats first agree to sweeping, tough new measures against illegal migration.

With the US in an election year that could again pit Biden against Donald Trump, Ukraine's President Volodymyr Zelensky has warned that a Trump return to the White House would likely bring a "different policy" on the war.