Kyiv is pushing Washington and London to lift a restriction on firing arms made by those countries, with Russian President Vladimir Putin warning that giving Ukraine the green light would mean NATO was "at war" with Moscow.

British media reported that Biden, who is wary of provoking a nuclear conflict, was ready to let Ukraine deploy British and French missiles using US technology but not US-made missiles themselves.

The talks come at a time when Biden is on his way out of office and November's US election is a toss-up between Democrat Kamala Harris and Republican Donald Trump.

Trump repeatedly refused to take sides on the war during a debate with Harris on Tuesday, saying only: "I want the war to stop."

Starmer is set to meet Biden in the Oval Office at 4:30 pm (2030 GMT) but has no scheduled meetings at this stage with Trump or Harris, both of whom will be on the campaign trail on Friday.

"These are strategic meetings to discuss Ukraine and to discuss the Middle East, and so it'll be at that level of strategic discussion that we'll be involved in tomorrow with the president," Starmer said Thursday.

His visit -- his second to Washington since his Labour party stormed to victory in July after 14 years -- is also aimed at papering over differences on the war in Gaza.

Starmer's government last week announced restrictions on some weapons to Israel, voicing concern that they could be used to violate international humanitarian law.

The White House has declined to criticize Britain's decision, but Politico reported that Washington had asked London what it would take to change its decision -- with the answer being a ceasefire in Gaza.