British Foreign Secretary David Cameron on a visit to Bulgaria on Wednesday urged members of the US Congress to "do the right thing" and approve a Ukraine aid package.

The Republican leader of the US House of Representatives on Tuesday blocked war aid for Ukraine, ignoring President Joe Biden's plea that passing the bill was vital for standing up to "Russian dictator" Vladimir Putin.

The bill was approved in the Senate earlier Tuesday. It includes $95 billion in funding, mostly for the security of pro-Western Ukraine, as well as for the top US strategic priorities of Israel and Taiwan.

"I urge members of Congress in the United States who'll be looking at this today to vote for their package," Cameron told reporters in Sofia.

"We appeal to them to do the right thing to stop aggression, to be on the side of freedom, to stand up for a country that's defending its borders," he added.

He warned approving the package was "absolutely crucial for American security" and "the whole world" would watch Congress' decision.

"The lessons of history are clear -- if you allow a dictator like Putin to take over part of another country, he won't stop there, he will come back for more," he said.

Cameron is visiting Bulgaria and then Poland this week to shore up support for Ukraine and discuss tackling migration. After that, he will attend the Munich Security Conference in Germany.

US aid to Ukraine has been paralysed for months by chaos in Congress, even as Kyiv begs for help to counter increased Russian attacks.

At the White House, Biden said that helping US allies -- and particularly coming to the aid of Ukraine as it struggles to fend off a two-year Russian invasion -- is a fundamental responsibility.