Ukraine's president is expected to intensify pleas for Nato allies to help halt Russian attacks when he addresses the US Congress by video-link later.
Volodymyr Zelensky is likely to repeat his request for a no-fly zone, in his latest speech to a national parliament.
His address comes with President Joe Biden set to announce an extra $800m (£612m) in military aid to Ukraine.
The money will go towards anti-armour and anti-aircraft weapons, such as Stingers and Javelins, US media report.
The funding is covered by a spending bill on humanitarian, defensive and economic assistance to Ukraine that was approved by Congress last week.
Signing the bill on Tuesday, Mr Biden said that Russian President Vladimir Putin's attack on Ukraine had united people across the world.
Mr Zelensky has repeatedly called on Nato to impose a no-fly zone over his country's airspace, but Nato has refused.
A no-fly zone over Ukraine would mean that Nato forces would have to engage directly with any Russian planes spotted in those skies and shoot at them if necessary.
In addition to a no-fly zone, the Ukrainian president has also asked the US and the EU for Polish MiG-29 fighter jets, but this has been rejected by Mr Biden over fears this would pull Nato members into the war.
Mr Biden is set to travel to Brussels next week to meet Nato allies and participate in a summit of European Union leaders.
The US president will "discuss ongoing deterrence and defence efforts," and reaffirm his country's commitment to its Nato allies, White House press secretary Jen Psaki has said.
Afterwards, the Czech leader told Ukrainians that they were "not alone". The group are the first Western leaders to visit Ukraine since Russia invaded last month.