US says it's preparing for 'significant' Iran attack on Israel as early as ...

The White House is warning that the United States assesses Iran could launch a retaliatory attack on Israel as early as "this week," and that the U.S. has to be prepared for an attack that could be "significant."

The warning comes as the U.S. has bolstered its force posture in the Middle East and has been very public in announcing its military moves -- something U.S. officials say is intended to deter Iran from possibly attacking and de-escalate tensions in the region.

That includes the Pentagon's announcement Sunday that the aircraft carrier USS Abraham Lincoln's arrival to the region was being "accelerated," as well as the rare public announcement that the guided missile submarine USS Georgia was being sent to the Middle East from its current deployment.

The U.S. assessment is in line with a reported Israeli assessment of a possible Iranian retaliatory attack as soon as this week, National Security Council spokesperson John Kirby told reporters Monday.

"We share the same concerns and expectations that our Israeli counterparts have with respect to potential timing here, could be this week," Kirby said.

"We have to be prepared for what could be a significant set of attacks," he added.

A Hezbollah commander, Fouad Shukr, and a top Hamas political leader, Ismail Haniyeh, were killed in separate incidents last month. Israel took responsibility for the strike that killed Shukr but has not said if it was also behind the attack that killed Haniyeh in Tehran, which Iran has blamed on Israel.

The recent assassinations of Shukr in Beirut and Haniyeh in Tehran have the Middle East on edge that Iran could retaliate against Israel by once again launching a strike toward Israel, as it did in mid-April.

On Monday, President Joe Biden spoke with the leaders of France, Germany, Italy and the United Kingdom to discuss the escalating tensions in the Middle East, and the increased force posture by the U.S. in the region.

"The president is confident that we have the capability available to us to help defend Israel, should it come to that," Kirby said.

"Nobody wants to see it come to that, which is why we continue to have these diplomatic conversations in earnest over the last few days to see what can be done to de-escalate this situation," he continued.

U.S. officials told ABC News that the announcement about the USS Georgia's deployment was intended as a message of deterrence to Iran about the continued presence of the U.S. military in the region, and that the United States is capable of surging military resources as needed.

In April, hundreds of Iranian drones and ballistic missiles were brought down by a combination of U.S. and Israeli aircraft, as well as Israeli and U.S. air defense systems, officials have said.

Ahead of that attack, the U.S. had quietly moved in additional aircraft and vessels to the region to assist Israel. This time, the United States has been public in announcing it was sending an additional squadron of Air Force F-22 aircraft, carrier-based Navy F/A-18s to a base on land, and deploying additional destroyers and the Lincoln to the region.

U.S. officials said the public announcements are intended to send a message to Iran that American military capabilities could be used against an Iranian attack.

One U.S. official indicated the deployment of the USS Georgia -- and the 154 Tomahawk land-attack cruise missiles aboard -- also sends a strong message of significant offensive capability.

The Lincoln strike group is currently in the South China Sea and may take some time to arrive in the Middle East to replace the aircraft carrier USS Theodore Roosevelt, currently off the coast of Oman.

One U.S. official said its arrival will give U.S. military planners more options for carrier operations as the situation develops in the coming weeks, which could impact whether there is a simple handoff or if both carriers end up operating in the region.

"We obviously don't want to see Israel have to defend itself against another onslaught, like they did in April. But if that's what comes at them, we will continue to help them defend themselves," Kirby said.

On Monday, the State Department said it would continue its diplomatic push to encourage Iran to scale down any retaliation.  

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

Multiple officials within the department say they are still cautiously optimistic Iran will limit the scope of its retaliation and hope it will avoid significant escalation out of concern it would disrupt cease-fire deal talks the U.S., Egypt and Qatar aim to relaunch on Thursday.

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

However, Hamas issued an announcement on Sunday saying it would not participate in the upcoming round of negotiations, casting significant doubt over whether talks would indeed resume.

A public spat playing out between Israeli Prime Minister Benjamin Netanyahu and Israeli Defense Minister Yoav Gallant over support for a hostage release and cease-fire deal also threatens to undercut messaging to Iran signaling that a deal was in reach.

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