Ukrainian President Petro Poroshenko is to begin a key visit to the US to seek further support to tackle what he describes as Russian aggression.
Mr Poroshenko will hold talks with US President Barack Obama before addressing a joint session of Congress.
Mr Poroshenko is flying to the US from Canada, where he told MPs Ukraine had bid “the last farewell” to the USSR after signing an EU association deal.
Ukraine accuses Russia of supporting rebels in its east. Moscow denies this.
More than 3,000 people have died in fighting between Ukrainian government forces and pro-Russian rebels in the eastern Donetsk and Luhansk regions since April.
A fragile ceasefire agreed on 5 September is holding, despite accusations of shelling by both sides.
On Tuesday, Ukraine’s MPs approved a bill granting self-rule to parts of the Donetsk and Luhansk regions – a move described as “capitulation” by some lawmakers.
The unrest in the east followed Russia’s annexation of Ukraine’s southern Crimea peninsula in March.
In Washington, Mr Poroshenko will also give a speech at the influential Atlantic Council think-tank.
During the state visit he is expected to push for closer political and economic ties between his former Soviet republic and the West, and seek further financial support for Ukraine’s struggling economy.
Mr Poroshenko has also been pressing for military assistance from the US to help defend Ukraine.
President Obama – alongside with many other Western leaders – has condemned Russia’s actions in Ukraine, but stressed that any military support would only include non-lethal equipment.
Both the US and the EU have recently imposed a new round of sanctions against Russia over its role in the Ukraine crisis.
Addressing the Canadian parliament on Wednesday, Mr Poroshenko said Ukraine had “crossed the Rubicon” by ratifying a day earlier the association and free trade agreement with the EU.
“This was Ukraine’s last ‘farewell’ to the Soviet Union,” he said to loud cheering and applause from Canadian lawmakers.
The association agreement aims to bring Ukraine closer to the EU and away from Russia’s sphere of influence.
The deal lies at the root of Ukraine’s crisis. It was former Ukrainian President Viktor Yanukovych’s refusal to sign it last November that triggered mass protests and his eventual fall from power.