Israeli forces have “expanded operations into central Gaza," Israel Defense Forces spokesman Rear Adm. Daniel Hagari said.

In Khan Younis in southern Gaza, the Israelis "are fighting with new methods" and “constantly adjusting our tactics based on the needs of the military operations,” Hagari said.

And in northern Gaza, Israeli forces have "attacked an array of Hezbollah targets in Lebanon," he said.

-ABC News’ Jordana Miller

About 80,000 vials of the measles mumps and rubella vaccine, also called the MMR vaccine, have been delivered to Gaza, according to the United Nations Relief and Works Agency for Palestine Refugees in the Near East.

The MMR vaccine is routinely given to children starting at 12 months old to 15 months old and again at 4 years old to 6 years old.

Israeli Minister for Strategic Affairs Ron Dermer, a key ally of Israeli Prime Minister Benjamin Netanyahu, will meet with Secretary of State Antony Blinken and national security adviser Jake Sullivan at the White House on Tuesday afternoon, according to administration officials.

The meeting will cover "a number of matters related to the conflict in Gaza and the return of hostages held by Hamas," according to National Security Council spokesperson Adrienne Watson.

Dermer was the Israeli ambassador to the U.S. from 2013 to 2021. He now serves in Netanyahu's government and is considered a close adviser to the prime minister.

-ABC News’ Arthur Jones, Lauren Peller and Jay O'Brien

On Christmas Day, 60 trucks crossed into Gaza via Egypt's Rafah border crossing, and an additional 60 trucks entered Gaza through Israel’s Kerem Shalom crossing, said Wael Abu Omar, the Palestinian spokesman for the Rafah crossing.

On Christmas Eve, the Royal Jordanian Air Force conducted its seventh airdrop of humanitarian aid into Gaza, the U.S. Embassy of Jordan said.

Gadi Hagi, a 73-year-old American-Israeli hostage and member of Kibbutz Nir Oz, has been confirmed dead, the kibbutz said.

Hagi was killed on Oct. 7 at the kibbutz and his body was taken to Gaza where it's still being held, according to a kibbutz spokesperson.

Hagi’s wife, 70-year-old Judy Weinstein, is wounded and still being held hostage, the kibbutz said.

Hagi and his wife were shot and kidnapped on Oct. 7, according to the Hostage Center.

"Gadi was a man full of humor who knew how to make those around him laugh," the Hostage Center said in a statement. "A musician at heart, a gifted flautist, he played in the IDF Orchestra and was involved with music his whole life."

Hagi was a father of four and a grandfather of seven.

Hagi reportedly has ties to New York.

"May Gadi's memory be a blessing," New York Gov. Kathy Hochul wrote on social media. "There are still many hostages -- including many with New York connections -- being held in Hamas captivity."

President Joe Biden said he was "heartbroken by the news."

"We continue to pray for the well-being and safe return of his wife, Judy," Biden said in a statement. "We are praying for their four children, seven grandchildren, and other loved ones and are grieving this tragic news with them."

Biden said Hagi's daughter joined, via phone, his meeting last week with families of hostages.

"Those families bravely shared with me the harrowing ordeal that they have endured over the past months as they await news of their loved ones," Biden said. "I reaffirm the pledge we have made to all the families of those still held hostage: we will not stop working to bring them home."