Ukraine’s President Volodymyr Zelensky is set to make a virtual address to the US Congress on Wednesday.
Mr Zelensky is expected to reiterate his plea for a no-fly zone, increasing pressure on the US and its allies.
The address comes as US President Joe Biden is set to announce an additional $800m (£612m) in military assistance 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.
In the past year, the Biden administration has provided $1.2bn in weapons for the country, including Mi-17 helicopters, patrol boats and small arms such as grenade launchers and machine guns, the New York Times reports.
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.
On Tuesday, the prime ministers of Poland, Slovenia and the Czech Republic met Mr Zelensky in the evening as a curfew began in the Ukrainian capital, Kyiv.
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.
War in Ukraine: More coverage
