Israel-Gaza updates: Netanyahu says Israel 'can't be flexible' on some issues

Several U.S. officials are headed to the Middle East this week in a bid to de-escalate regional tensions and try to salvage hostage negotiations, as the window for a deal appears to be closing.

CIA Director Bill Burns is expected to arrive in Doha, Qatar, this week, where he will lead a crucial meeting on the hostages, according to a U.S. official. It’s not clear, however, whether a representative of Hamas will attend.

Meanwhile, Brett McGurk, Biden’s top adviser on the Middle East at the White House, was expected to travel separately to Cairo, according to the U.S. official.

Axios first reported the travel plans for Burns and McGurk, noting that McGurk’s plan was to nail down a security plan for the Egypt-Gaza border.

The diplomatic trip also comes as the U.S. has been scrambling to revive a coalition of countries that helped to defend Israel last April during an attack by Iran.

Israel has been bracing for Iran to launch a retaliatory attack following the assassination of a senior Hamas official in Tehran.

The U.S. official acknowledged "there have been complications" with getting some of the Arab countries on board but added they've been "able to put in place preparations" to defend Israel successfully.

-ABC News' Anne Flaherty

The leaders of the U.S., U.K., France, Germany and Italy called on Iran to "stand down" and expressed their support for Israel's defense "against Iranian aggression" during a call on Monday, according to a joint statement released by the White House.

“We called on Iran to stand down its ongoing threats of a military attack against Israel and discussed the serious consequences for regional security should such an attack take place," the statement said.

The leaders also expressed their support for ongoing efforts to reach a cease-fire and hostage release deal in Gaza, according to the statement.

-ABC News' Justin Gomez

As the Middle East continues its uneasy wait for Iran's response to the killing of Hamas political leader Ismail Haniyeh, the State Department is pressing on with its high-stakes diplomatic campaign to constrain military action from Tehran amid fresh waves of uncertainty.

"We continue to work diplomatically to prevent any major escalation in this conflict,” deputy spokesperson Vedant Patel told reporters Monday. "We obviously don't want to see any kind of attack or response happen in the first place."

Multiple officials within the State Department said they are still cautiously optimistic that Iran will limit the scope of its retaliation, but that they increasingly expect the country will strike at Israel before Thursday -- the date the Biden administration, along with Egypt and Qatar, set to relaunch hostage/cease-fire deal talks in hopes of bringing Israel and Hamas back to the table for a final push.

A joint statement issued by the mediators last week was designed not only to pressure the parties involved, but as a message to Iran that an agreement was in the offing meant to persuade the country against military action that could scuttle a deal, according to an official.

National Security Council spokesperson John Kirby also publicly warned Monday that Iranian military action could impede progress at a critical point in the negotiations.

However, Hamas' earlier announcement that it would not participate in the round of negotiations and public infighting among top Israeli officials have cast significant doubt over whether the Thursday meeting will even happen -- undercutting the administration's intended message to Tehran.

At the podium Monday, Patel said mediators "fully expect talks to move forward as they should" in order to "bring this deal to conclusion."

He declined to say whether Hamas or Israel was the bigger impediment.

"I'm not going to color it one way or the other," Patel said while noting that "the prime minister of Israel immediately welcomed this initiative and confirmed that the Israeli team will be there, and they'll be prepared to finalize the details of implementing the deal."

-ABC News' Shannon K. Kingston

A United States assessment shows a retaliatory attack by Iran and its proxies against Israel could be launched "this week," the White House said Monday.

"We share the same concerns and expectations that our Israeli counterparts have with respect to potential timing here. Could be this week," National Security Council spokesperson John Kirby told reporters. "We're continuing to watch it very, very closely."

Kirby said it's difficult to ascertain what a potential attack could look like at this time but that "we have to be prepared for what could be a significant set of attacks."

Meanwhile, Israel Defense Forces spokesperson Daniel Hagari told reporters on Monday that Israel remains "on high alert."

"We take seriously the threats of our enemies and that is why we are on high alert offensively and defensively," he said.

Hagari said the IDF will "work hard to give the public time to get organized."

-ABC News' Justin Gomez