Ukrainian President Volodymyr Zelenskyy could travel to Washington, meet U.S. President Joe Biden and visit Congress on Wednesday, sources familiar with the situation said, in what would be Zelensky's first known trip outside his country since the onset of Russia-Ukraine conflict.

The visit by Zelenskyy would coincide with Biden's intent to send the Kyiv government an additional $1.8 billion defense assistance package headlined by the Patriot missile systems, CNN reported, to protect it from heavy Russian bombardment. CNN also reported, citing two sources, that Zelenskyy was already on his way to Washington.

Zelenskyy's spokesman did not respond to a request for comment. U.S. House of Representatives Speaker Nancy Pelosi's office did not immediately respond to a request for comment. Earlier on Tuesday, Pelosi said in a letter that there would be a session of Congress on Wednesday night which would have a "very special focus on democracy."

Zelenskyy's trip abroad 10 months into the war was expected to include a visit to lawmakers at the U.S. Capitol, a source familiar with the planning said on Tuesday. And the trip has not been confirmed and security concerns could force a change in plans, the source said.

Zelensky made a surprise trip to troops in the battered frontline city of Bakhmut in Ukraine's eastern Donetsk region, his office said on Tuesday. The city, in recent weeks, has been the epicenter of fighting between Ukrainian and Russian troops. 

During his visit, Zelenskyy met with personnel of a mechanized brigade involved in the confrontation with Russian forces on the approaches to the city. He listened to the commander's report on the operational situation on the frontline and thanked the Ukrainian military for their courage, resilience and strength demonstrated during the fighting. 

He urged the troops to keep up their spirits as the battle for Bakhmut, one that has come to symbolize the grinding brutality of the war, enters its fifth month. He also handed out medals to soldiers from the mechanized, motorized infantry, mountain assault, tank, artillery and air mobile units with state awards, video released by his office showed.

Earlier, he repeated calls to the West for more weaponry, including air defence systems, after Russian drones hit energy targets in a third air strike on power facilities in six days.

A U.S. government funding bill in the Senate includes $44.9 billion in emergency assistance to Ukraine and NATO allies. The money would be used for military training, equipment, logistics and intelligence support, as well as for replenishing U.S. equipment sent to the government in Kyiv.

Washington is also close to finalizing plans to send the Patriot missile defence system to Ukraine, according to sources, but the Kremlin has warned the U.S.-supplied equipment would be a legitimate target for Russian strikes against Ukraine.

Kyiv has argued it needs Western help to strengthen its air defenses against repeated Russian strikes on Ukraine's energy infrastructure, which have cut electricity and water supplies in part of Ukraine amid winter. Prime Minister Denys Shmyhal said Ukrainians should prepare for new Russian attacks on energy infrastructure in the following months.

(With input from Reuters)