Ukrainian President Volodymyr Zelenskyy is traveling to the U.S. where he will meet President Joe Biden and visit Congress on Wednesday.
It will be Zelenskyy's first known overseas trip since Russia's invasion began on Feb. 24.
Zelenskyy said he was going to Washington for talks with Biden to strengthen Ukraine's "resilience and defense capabilities" and address the U.S. Congress.
During the visit, Biden will announce a package of military assistance for Ukraine valued at nearly $2 billion that will include a Patriot missile battery to help it defend itself against barrages of Russian missiles, a senior U.S. official said.
Zelenskyy's visit, which had been organized in secret until details emerged Tuesday night, was expected to last several hours.
He will hold talks with Biden and top national security aides at the White House, participate in a joint news conference with Biden, and then go to Capitol Hill to address a joint session of the U.S. Senate and House of Representatives.
White House press secretary Karine Jean-Pierre said in a statement that Biden invited Zelenskyy to Washington "to underscore the United States' enduring commitment to Ukraine."
"The visit will underscore the United States' steadfast commitment to supporting Ukraine for as long as it takes, including through the provision of economic, humanitarian, and military assistance," she said.
Zelenskyy's trip takes place 300 days after Russia invaded Ukraine with the aim of capturing Kyiv in days, a goal that quickly fizzled as the strength of Ukraine's response – aided by billions in weaponry from the United States and allies – made the Ukrainians unexpectedly tough opponents.
Biden's message to Zelenskyy will be one of resolve and conviction, the U.S. official said.
Biden will be face-to-face with the man he has spoken with regularly over the past 10 months but not met in person since the war broke out.
With Biden's firm support, the West has rallied behind Ukraine and sought to isolate Russia without getting involved in a direct conflict with it.
Biden will not use the talks to push Zelenskyy toward the negotiating table with Russian President Vladimir Putin, the U.S. official said.
The Biden administration has provided about $20 billion in military assistance to Ukraine, including artillery ammunition, and munitions for NASAMS air defense systems and for high mobility artillery rocket systems (HIMARS).
Zelenskyy has repeated calls to the West for more weaponry including air defense systems after Russian drones hit energy targets in a third strike on power facilities in six days.
Russia has warned that Ukraine's U.S.-supplied equipment would be a legitimate target for Russian strikes.
Zelenskyy had earlier made a surprise trip to the eastern frontline city of Bakhmut, his office said, underlining Russia's stuttering but persistent attempts to capture it.
In his nightly video address, Zelenskyy referred to the visit as a trip to "Fortress Bakhmut" in Donetsk, a province Russia claimed in September. Most countries reject Russia's claim as an illegal occupation.
Dressed in combat khaki, Zelenskyy handed out medals to soldiers in a tumble-down industrial complex to applause, a video released by his office showed.
In contrast, Putin awarded medals in the comfort of the Kremlin to the Russian-appointed leaders of four regions of Ukraine that Russia has claimed to have annexed since invading its neighbor.
Video footage released on Ukrinform TV, part of Ukraine's state news agency, showed servicemen in Bakhmut handing Zelenskyy a Ukrainian flag with their signatures on it.
"We will turn it over to the Congress and to the U.S. president from the guys," Zelenskyy said in the video. "We are grateful for the support. But it's not enough," he added.
He has 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.
"The east is holding out because Bakhmut is fighting. In fierce battles and at the cost of many lives, freedom is being defended here for all of us," Zelenskyy wrote on the Telegram messaging app.
The U.S. Senate has advanced a government-funding bill that 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 Ukraine.
The World Bank on Tuesday said it had approved an additional financing package for Ukraine totaling $610 million to address urgent relief and recovery needs.
Kyiv has argued it needs Western help to strengthen its air defenses as Russian strikes have repeatedly cut electricity and water supplies in subzero winter temperatures.
Ukrainian officials say Russia's missiles and bombardments are aimed at breaking the will of civilians.
Prime Minister Denys Shmyhal said Ukrainians should prepare for new attacks by Russia on energy infrastructure because it wanted them to spend Christmas and the New Year in darkness.
