The father of American-Israeli hostage Edan Alexander issued an emotional request on Sunday to President Biden, President-elect Trump and Israeli Prime Minister Benjamin Netanyahu, telling the leaders to act now to bring the hostages home "before it's too late."

A day after seeing his son for the first time in a year in a propaganda video released by Hamas' military wing, Adi Alexander of New Jersey spoke at a rally in New York City's Central Park, saying, "No father should hear his child plead for his life like that."

"President Biden, President Trump, Prime Minster Netanyahu, I call on all of you to act," Alexander said. "This is not a moment for politics or hesitation. This is a moment of courage, collaboration and decisive action."

He appealed to Biden to use the United States' influence "to negotiate a deal before it's too late."

Directing his words to Trump, he said, "You do not have to wait until January to make an impact. The world is watching. Act now."

To Netanyahu, Alexander said, "The fate of the hostages, including my son, rests in your hands. You have the power to bring them home. Don't let this opportunity slip away."

Edan Alexander, 20, was serving in the Israeli military and stationed near Gaza when he was taken captive by Hamas terrorists on Oct. 7, 2023.

The White House issued a statement, saying, it has been in touch with the Alexander family and called the hostage video a “cruel reminder of Hamas’s terror against citizens of multiple countries, including our own.”

“The war in Gaza would stop tomorrow and the suffering of Gazans would end immediately-- and would have ended months ago-- if Hamas agreed to release the hostages,” White House National Security Council spokesperson Sean Savett said in a statement. "It has refused to do so, but as the President said last week, we have a critical opportunity to conclude the deal to release the hostages, stop the war, and surge humanitarian assistance into Gaza. This deal is on the table now."

Israeli Prime Minister Benjamin Netanyahu will hold a security meeting Sunday night to discuss the issue of the hostages, as well as Lebanon and Syria, an Israeli official told ABC News.

-ABC News' Jordana Miller

UNRWA Commissioner-General Philippe Lazzarini on Sunday announced a pause to Gaza aid deliveries via the strip's main crossing point, citing serious threats to the safety of staff.

The road out of the Kerem Shalom crossing "has not been safe for months," Lazzarini said in a post to X.

"This difficult decision comes at a time hunger is rapidly deepening," Lazzarini said. "The delivery of humanitarian aid must never be dangerous or turn into an ordeal."

The UNRWA chief said a "large convoy of aid trucks was stolen by armed gangs" on Nov. 16, with several more aid trucks taken on Saturday.

Lazzarini also said that Israel's "ongoing siege" of Gaza, "hurdles" put in place by Israeli authorities and "⁠political decisions to restrict the amounts of aid" were among the other problems facing U.N. staff.

"The humanitarian operation has become unnecessarily impossible," he wrote. "The responsibility of protection of aid workers [and] supplies is with the state of Israel as the occupying power."

-ABC News' Somayeh Malekian

Israeli Defense Minister Israel Katz said he spoke with the family of Israeli-American hostage Edan Alexander, a video of whom was released by Hamas on Saturday.

"The brutal video that was released is part of psychological warfare, but it is an important and moving sign of life for us and for his family," Katz wrote on X.

"The hostages and their families are going through terrible suffering," he added. Israeli authorities "are working tirelessly to return all the kidnapped people home," Katz wrote.

Alexander, who grew up in New Jersey, was a serving Israeli soldier positioned on the Gaza frontier during Hamas' Oct. 7, 2023, surprise attack.