National security adviser Jake Sullivan will meet families of hostages at the White House on Monday, which is one day after the war reaches the six-month mark, a senior administration official said.

President Joe Biden on Friday wrote letters to the president of Egypt and the emir of Qatar on the state of the talks, and he urged them to secure commitments from Hamas to agree to and abide by a deal, the official added.

"The president made clear that everything must be done to secure the release of hostages, including American citizens, now held by Hamas terrorists for nearly six months," the senior administration official said.

"They discussed the importance of fully empowering Israeli negotiators to reach a deal, which in its first phase would secure the release of women, elderly, sick and wounded hostages," the official said.

A new round of talks will take place this weekend in Cairo.

-ABC News’ Selina Wang

The Israeli Defense Forces issued a new statement in English calling the Israeli military’s strikes that killed seven World Central Kitchen aid workers on Monday a "tragedy."

"It was a terrible chain of errors and it should never have happened," the IDF said. "The IDF takes full responsibility for this regrettable loss of life."

The IDF said earlier that the airstrike came after Israeli forces misidentified a WCK worker in the convoy as a Hamas gunman.

The IDF said WCK correctly coordinated its movements with the IDF prior to the night the workers were killed and that there was a "comprehensive plan" in place for the WCK workers’ movements on Monday.

-ABC News’ Ellie Kaufman

U.S. officials are reviewing Israel's report on the Israel military’s attack on World Central Kitchen aid workers "very carefully" and "will be discussing its conclusions with Israeli officials and with humanitarian organizations in the days to come," Secretary of State Antony Blinken told reporters.

The Israel Defense Forces said its airstrike in Gaza that killed seven WCK aid workers on Monday came after Israeli forces misidentified a WCK worker in the convoy as a Hamas gunman.

Blinken said Israeli Prime Minister Benjamin Netanyahu "indicated" to President Joe Biden in their Thursday call "that Israel would be making further changes to its procedures to make sure that those who are providing assistance to people who so desperately need it in Gaza are protected."

"It's very important that Israel is taking full responsibility for this incident. It's also important that it appears to be taking steps to hold those responsible accountable," Blinken said. "Even more important is making sure that steps are taken going forward to ensure that something like this can never happen again."

Blinken said the U.S. would be "looking to see not just what steps are being taken, but the results that follow" from potential changes to Israeli military operations.

-ABC News’ Chris Boccia

White House national security communications adviser John Kirby warned Friday that if the U.S. doesn’t "start seeing meaningful changes in the way Israel is prosecuting these [military] operations [in Gaza] and allowing for humanitarian assistance [in Gaza], and working toward a hostage deal and cease-fire, then we’re going to have to make changes in our Gaza policy."

In his interview with ABC News' "Good Morning America," Kirby would not say if those changes in Gaza policy would mean conditioning U.S. aid.

But Kirby said President Joe Biden was very clear on his call Thursday with Israeli Prime Minister Benjamin Netanyahu that the U.S. must "see some changes."

"We’ve got to see the humanitarian situation improve in Gaza, or otherwise we will have to try to take a look at our own policy and make decisions, and change the way that we’re supporting Israel," Kirby said.

3:07

White House official on how Israel must change conduct of Gaza war

Top national security spokesperson John Kirby shares more details about President Joe Biden’s conversation with Israeli Prime Minister Benjamin Netanyahu and what happens next.

The U.S. still wants an immediate cease-fire in exchange for the release of the Israeli hostages and for getting more aid into Gaza, Kirby stressed. U.S. officials will be among the negotiators meeting this weekend in Cairo, he said.