WASHINGTON — Ukrainian President Volodymyr Zelensky is preparing to visit Washington on Wednesday, according to three AP sources, in his first known trip outside the country since Russia’s invasion began in February.

Two congressional sources and one person familiar with the matter confirmed plans for the visit. They spoke on the condition of anonymity because of the highly sensitive nature of the trip. They said Zelensky’s visit, while expected, could still be called off at the last minute due to security concerns.

Ukrainian President Volodymyr Zelensky looks on as he meets soldiers at the site of the heaviest battles with the Russian invaders on Tuesday in Bakhmut, Ukraine. Ukrainian Presidential Press Office via Associated Press

The visit to Washington is set to include an address to Congress on Capitol Hill and a meeting with President Biden. It comes as lawmakers are set to vote on a year-end spending package that includes about $45 billion in emergency assistance to Ukraine and as the U.S. prepares to send Patriot surface-to-air missiles to the country to help stave off Russia’s invasion.

The visit comes a day after Zelensky made a daring and dangerous trip to what he called the hottest spot on the 1,300-kilometer (800-mile) front line, the city of Bakhmut in Ukraine’s contested Donetsk province, where he praised Ukrainian troops for their “courage, resilience and strength” as artillery boomed in the background.

The Ukrainian leader told the troops he passed through Sloviansk, Kramatorsk and Druzhkivka to reach Bakhmut in an unannounced trip that appeared designed to show Moscow’s failure to capture the city and dishearten the Russians trying to surround it.

“Bakhmut Fortress. Our people. Unconquered by the enemy. Who with their bravery prove that we will endure and will not give up what’s ours,” he wrote on his Telegram channel, thanking the troops for “the courage, resilience and strength shown in repelling the enemy attacks.

“Since May, the occupiers have been trying to break our Bakhmut, but time goes by and Bakhmut is already breaking not only the Russian army, but also the Russian mercenaries who came to replace the wasted army of the occupiers,” he said.

Russia’s invasion, which began Feb. 24, has lost momentum. The illegally annexed provinces of Donetsk, Kherson, Luhansk and Zaporizhzhia remain fiercely contested. Capturing Bakhmut would sever Ukraine’s supply lines and open a route for Russian forces to press on toward cities that are key Ukrainian strongholds in the Donetsk province.

In a video released by his office from the Bakhmut visit, Zelensky was handed a Ukrainian flag and alluded to delivering it to U.S. leaders.

“The guys handed over our beautiful Ukrainian flag with their signatures for us to pass on,” Zelensky said in the video. “We are not in an easy situation. The enemy is increasing its army. 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.”

The latest tranche of U.S. funding would be the biggest American infusion of assistance yet to Ukraine, above even Biden’s $37 billion emergency request, and ensure that funding flows to the war effort for months to come.

On Wednesday, the U.S. was also set to announce that it will send $1.8 billion in military aid to Ukraine in a major package that will for the first time include a Patriot missile battery and precision-guided bombs for its fighter jets, U.S. officials said.

The aid signals an expansion by the U.S. in the kinds of advanced weaponry it will send to Ukraine to bolster its air defenses against what has been an increasing barrage of Russian missiles in recent weeks. The package will include about $1 billion in weapons from Pentagon stocks and $800 million in funding through the Ukraine Security Assistance Initiative, officials said.

The decision to send the Patriot battery comes despite threats from Russia’s Foreign Ministry that the delivery of the advanced surface-to-air missile system would be considered a provocative step and that the Patriot and any crews accompanying it would be a legitimate target for Moscow’s military.

It’s not clear exactly when the Patriot would arrive on the front lines in Ukraine, since U.S. troops will have to train Ukrainian forces on how to use the high-tech system. The training could take several weeks, and is expected to be done in Germany. To date, all training of Ukraine’s forces by the U.S. and its Western allies has taken place in European countries.

Also included in the package will be an undisclosed number of Joint Direct Attack Munitions kits, or JDAMs. The kits will be used to modify massive bombs by adding tail fins and precision navigation systems so that rather than being simply dropped from a fighter jet onto a target, they can be released and guided to a target.

The visit comes at an important moment as the White House braces for greater resistance from a Republican-controlled House that’s signaled it will put more scrutiny on aid for Ukraine in the new Congress. GOP leader Kevin McCarthy has said his party’s lawmakers will not write a “blank check” for Ukraine.

Biden and Zelensky frequently have held phone calls in coordination with the White House announcing new tranches of military assistance for Ukraine. The calls have been mostly warm, with Biden praising Ukraine for remaining steadfast against the Russians and Zelensky thanking the U.S. president for support.

House Speaker Nancy Pelosi, who visited Zelensky earlier this year in Kyiv, encouraged lawmakers to be on hand for Wednesday evening’s session.

“We are ending a very special session of the 117th Congress with legislation that makes progress for the American people as well as support for our Democracy,” Pelosi wrote Tuesday in a letter to colleagues. “Please be present for a very special focus on Democracy Wednesday night.”

Later at the Capitol, Pelosi said of Ukrainians, “They are fighting for democracy for all of us.”

For his part, Russian President Vladimir Putin on Tuesday hailed the “courage and self-denial” of his forces in Ukraine – but he did so at a ceremony in an opulent and glittering hall at the Kremlin in Moscow, not on the battlefield.

Mercenaries from the Wagner Group, a shadowy Russian military contractor, are reported to be leading the charge in Bakhmut. Unverified videos on a popular Russian social media platform showed the Wagner Group’s leader, Yevgeny Prigozhin, standing near an artillery piece and saying he was ready to meet Zelensky in Bakhmut.

At the Kremlin ceremony, Putin presented awards to the Moscow-appointed heads of the four illegally annexed regions of Ukraine.

“Our country has often faced challenges and defended its sovereignty,” Putin said. “Now Russia is again facing such a challenge. Soldiers, officers and volunteers are showing outstanding examples of courage and self-denial on the front line.”

In a video address honoring Russia’s military and security agencies, he praised the security personnel deployed to the four regions, saying that “people living there, Russian citizens, count on being protected by you.”

Putin acknowledged the challenges faced by the security personnel.

“Yes, it’s difficult for you,” he said, adding that the situation in the regions is “extremely difficult.”

British authorities, meanwhile, gave a bleak assessment of how the war is going for Russia.

Some 100,000 Russian troops were “dead, injured or have deserted” in the invasion, U.K. Defense Secretary Ben Wallace said. Wallace didn’t give a figure for Ukrainian casualties, but the U.S. military recently put the estimated number of Ukrainian troops killed and wounded at about 100,000.

Losses in Russia’s military command have also taken a toll, as has the destruction of equipment. “Not one single operational commander then in place on Feb. 24 is in charge now,” Wallace told lawmakers in the House of Commons. “Russia has lost significant numbers of generals and commanding officers.”

“Russian capability has been severely hampered by the destruction of more than 4,500 armored and protected vehicles, as well as more than 140 helicopters and fixed wing aircraft,” Wallace said.

Ukraine’s counteroffensive has succeeded in recapturing large swaths of land. After 300 days of war, the U.K. Ministry of Defense tweeted, Ukraine has liberated about 54% of the maximum amount of extra territory Russia seized in the invasion. It didn’t say what portion of Ukrainian territory Russia controlled at the peak of its gains.

Russia now controls about 18% of internationally recognized areas of Ukraine, including those parts of the eastern Donbas and the Crimean Peninsula seized in 2014.

With the fighting in the east at a stalemate, Moscow has used missiles and drones to attack Ukraine’s power equipment, hoping to leave people without electricity as freezing weather sets in.

Life in the Ukrainian capital took a minor but welcomed step toward normality with the reopening of two of Kyiv’s main subway stations for the first time since the war began. The key hubs of Maidan Nezalezhnosti and Khreschatyk, like the capital’s other underground stations, have served as air raid shelters.

“It’s the feeling that despite everything, we are returning to a routine that we were used to,” said 24-year-old passenger Denys Kapustin. “This is very important.”

Castillo reported from Kyiv, Ukraine. Lolita C. Baldor and Tara Copp in Washington and Andrew Katell in New York contributed.