Lord David Cameron has urged US Republicans to back Ukraine as they hold out on authorising tens of billions of dollars in military support in the fight against Vladimir Putin.

The Foreign Secretary urged allies not to tell Kyiv they should negotiate with the Russian President during a visit to Washington DC for talks on Wednesday.

Efforts are intensifying to shore up support for Ukrainian President Volodymyr Zelensky as the spectre of a possible return of Donald Trump to the White House raises concern.

US President Joe Biden is battling to get his fresh military and economic aid package for Ukraine through the Republican-controlled House of Representatives.

Lord Cameron used his two-day visit to appeal to Republicans with an interview on Fox News, arguing the message if the support is not approved would be “really, extremely bad”.

“I’m more worried that we’re not going to back them enough,” he said, as he praised the “brave” and “united” Ukraine.

He said it is “about American security too”, saying Mr Putin will go after other European nations if he wins in Ukraine in a move that could ultimately draw in US troops if a Nato ally is attacked.

Lord Cameron added to Sky News: “There’s definitely a majority in here to back Ukraine but it’s made more complicated by the politics.”

He was asked what he would say to Republicans urging Kyiv to negotiate with Mr Putin in a deal that would see Russia gaining land.

He answered: “What I say to them is, ‘Look, of course one day we have to help bring this to an end, but right now the task is to support Ukraine, to help them in this fight, to help them through the winter.

“It shouldn’t be for us to say to the Ukrainians now is the time to make this proposal, or that proposal, right now what we’ve got to do is back them.”

The Foreign Secretary is expected to meet US secretary of state Antony Blinken and Republican and Democratic congressional leaders as part of the trip.

The crisis in the Middle East will also top discussions, as Israel widens its offensive into southern Gaza amid growing fears about the fate of civilians.