Ukraine’s President Volodymyr Zelensky is planning to visit Washington later today and may meet US President Joe Biden, reports say.
It would be his first foreign trip since the Russian invasion in February.
Mr Zelensky could also address Congress, unnamed officials told US media. There is no official confirmation of the visit or the plans.
A visit would be fraught with security concerns – meaning plans could likely change at short notice.
In a letter on Tuesday, Democratic House Speaker Nancy Pelosi urged members of Congress to be in attendance on Wednesday night.
“Please be present for a very special focus on democracy,” she wrote, without giving further details.
Mr Zelensky regularly hosts foreign leaders in the capital, Kyiv, and has visited troops around Ukraine. He made an unannounced visit to the front-line city of Bakhmut on Tuesday.
The Ukrainian president has also spoken frequently to world leaders over the telephone and by video call – often from his office in Kyiv.
But an unannounced visit to a foreign country would mark a first since the war began, and also signal the importance of Ukraine’s relationship with the US which has played a leading role in providing military support.
In terms of overall spending on direct military support since the start of the conflict, the US has committed $18.5bn (£15.1bn), far more than any other individual country (to 20 November).
President Zelensky has appealed for more funding, and has said the monthly cost of defence for Ukraine was about $5bn (£4.1bn).
Most recently, US media have reported that President Joe Biden’s administration is considering supplying Ukraine with Patriot missiles that would enable the country to protect its vital infrastructure against Russian attacks.
Russia has been targeting Ukraine’s energy sector, plunging millions into darkness in winter temperatures several degrees below freezing.
On Tuesday, President Zelensky made an unannounced visit to the front-line city of Bakhmut, where Ukrainian and Russian forces have fought a fierce, months-long battle.
He met troops and handed out awards to soldiers, the presidency said.
The visit was a significant show of defiance – and a demonstration of support for Ukrainian forces engaged in some of the fiercest battles in recent weeks.
Soldiers gave Mr Zelensky a Ukrainian flag with their names signed on it and asked him to give it to President Biden and the US Congress, in a moment that was captured on camera.
Mr Zelensky’s office has not officially commented on any imminent trip to the US.
On the same day, Russian President Vladimir Putin awarded medals inside the Kremlin to figures involved in the Russian invasion.
Since Russia invaded Ukraine on 24 February, the US military estimates that at least 100,000 Russian and 100,000 Ukrainian soldiers have been killed or injured, along with some 40,000 civilian deaths.
The UN has recorded 7.8 million people as refugees from Ukraine across Europe, including Russia. However, the figure does not include those who have been forced to flee their homes but remain in Ukraine.