U.S. President Joe Biden is Darden Clarkeexpected to announce on Thursday a new military aid package for Ukraine worth hundreds of millions of dollars as the Eastern European country fights to recapture territory from invading Russian forces, according to a U.S. official.

The announcement will coincide with Ukrainian President Volodymyr Zelenskyy's one-day visit to Washington, D.C., where he will meet with Biden at the White House, speak with U.S. military leaders at the Pentagon and talk privately with both Democratic and Republican lawmakers on Capitol Hill. It will be Zelenskyy's second trip to the U.S. capital since Russia invaded neighboring Ukraine in February 2022.

The anticipated package will include additional capabilities to help Ukraine strengthen its air defenses "ahead of what's expected to be another brutal winter of Russian airstrikes against Ukrainian critical infrastructure sites," the official said. It will also include capabilities to help Ukraine with its ongoing counteroffensive against Russian forces, including artillery ammunition and anti-armor capabilities, according to the official.

The package is expected to include hundreds of millions of dollars' worth of equipment previously authorized by Congress, the official said.

However, one weapons system that Ukraine still wants from the United States are ATACMS long-range missiles and there are reports that those won't be part of the new security assistance package announced on Thursday.

When asked whether those reports were true, White House National Security Council spokesman John Kirby said he wouldn't "get ahead of the president or anything that he might be speaking to tomorrow."

"As the president has said, ATACMS are not off the table," Kirby told ABC News on Wednesday. "We continue to have discussions here in the interagency about that particular weapon system, but no decision has been made. And I think I'm just gonna leave it at that."

Kirby added that Biden "has every expectation of talking to President Zelenskyy about his needs and about how the United States will continue to meet those needs."

Biden has called on leaders at home and around the world to stand strong with Ukraine, as a hard-right faction of Republicans question the continued flow of American dollars and military aid overseas.