Biden plans to urge Trump to keep supporting Ukraine

US National Security Adviser Jake Sullivan has said that President Joe Biden's top message during his meeting with President-elect Donald Trump will be his commitment to ensure a peaceful transfer of power, and he will also talk to him about what's happening in Europe, in Asia and the Middle East.

"President Biden will have the opportunity over the next 70 days to make the case to the Congress and to the incoming administration that the United States should not walk away from Ukraine, that walking away from Ukraine means more instability in Europe," Sullivan told CBS News' "Face the Nation" show on Sunday.

Sullivan's comments came as Russia and Ukraine launched record drone attacks on each other, with around 200 drones exchanged in total.

When asked if Biden would ask Congress to pass legislation to authorise more funding for Ukraine, Sullivan deferred.

"I'm not here to put forward a specific legislative proposal. President Biden will make the case that we do need ongoing resources for Ukraine beyond the end of his term," Sullivan said.

Trump's stance on Ukraine

The comments also came one day after Donald Trump's presidential transition effort distanced itself from comments made by a Republican operative who suggested Kiev should focus on peace and not restoring territory.

"Bryan Lanza was a contractor for the campaign," said the spokesperson, who declined to be named. "He does not work for President Trump and does not speak for him."

Trump always claimed he would end the war in Ukraine in one day, although he never explained how he would do so.

He also insisted that Russia wouldn't have attacked Ukraine had he been the US president at the time.