The visit has not yet been confirmed by Washington amid concerns over security.

Writing on Twitter, Zelenskyy said he was on his way to the US to "strengthen resilience and defence capabilities". 

He said he would discuss cooperation between the US and Ukraine, adding: "I will also have a speech at the Congress and a number of bilateral meetings."

Speaker of the US House of Representatives Nancy Pelosi earlier said there would be a session of Congress on Wednesday that would have a "very special focus on democracy".

US politicians are set to vote on a year-end spending package, including around $45 billion in emergency assistance to Ukraine. Meanwhile, the US is preparing to send surface-to-air missiles to aid the country in repelling Russia's invasion.

The funding would be the biggest American infusion of assistance yet to Ukraine, surpassing President Biden's $37 billion emergency request and will ensure funding flows to the war effort for months to come.

Zelenskyy has addressed various parliaments and international organisations by video throughout Russia's invasion and has sent his wife to foreign capitals to call for support.

A surprise visit to troops on the frontline

It comes after Zelenskyy made a surprise visit to troops in the frontline city of Bakhmut in Ukraine's contested Donetsk province.

Visiting the scene of some of the most intense combat since Russia invaded Ukraine, Zelenskyy praised his troops' "courage, resilience and strength".

In a video released by his office, Zelenskyy was handed a Ukrainian flag and hinted at delivering it to US leaders. 

"The guys handed over our beautiful Ukrainian flag with their signatures for us to pass on," he said.

"We are not in an easy situation. The enemy is increasing its army, and our people are braver and need more powerful weapons. We will pass it on from the boys to the Congress, to the president of the United States. We are grateful for their support, but it is not enough. It is a hint - it is not enough."

Sky News