Ukraine President Volodymyr Zelensky is going to Washington DC to try to rescue a threatened US defence package to Kyiv worth billions of dollars.
The aid has become embroiled in US domestic, partisan politics.
It will be Mr Zelensky’s third visit to the US since Russia’s February 2022 invasion of Ukraine.
The week is a crucial one for Ukraine, with the European Union also deciding whether to open formal talks on its accession to the bloc.
Hungarian Prime Minister Viktor Orban has signalled that he opposes the move, and has the power to block such a decision.
Mr Orban and Mr Zelensky had an apparently intense conversation when they met on Sunday at the inauguration of Argentina’s new president. The details of their discussion have not been revealed.
The Ukrainian president will arrive in Washington on Monday. As well as holding meetings with US President Joe Biden and Republican House Speaker Mike Johnson, he will address the Senate on Tuesday morning.
The White House said in a statement on Sunday that Mr Zelensky’s visit was meant “to underscore the United States’ unshakeable commitment to supporting the people of Ukraine as they defend themselves against Russia’s brutal invasion”.
The US military aid package, worth $60bn (£47.9bn; €55bn), is currently stalled in Congress, facing pushback from Republicans who argue that more money should be going to domestic security at the US-Mexico border.
A vote in the Senate last week saw a package, which included the funding, blocked.
Mr Biden has been urging lawmakers to approve the funds. In an impassioned televised address last Wednesday, he said the package could not wait and warned that Russia would not stop at victory over Ukraine.
Though Ukraine fended off Russia’s original attack, its much-vaunted counter-attack this year has stalled and there have been signs of fatigue from some of the Western nations which have stepped up to support it militarily.