Iran could carry out "significant" attacks on Israel as early as "this week," United States National Security Council spokesman John Kirby said on Monday.
"We have to be prepared for what could be a significant set of attacks," he told reporters, adding that Washington shared Israeli assessments that such a move "could be this week."
Kirby was speaking after US President Joe Biden held talks with the leaders of the United Kingdom, France, Germany and Italy in which he discussed the prospect of a ceasefire in Gaza and ways to de-escalate tensions across the Middle East.
The call, Kirby said, was "largely for all the leaders to repeat what they have said before in terms of reaffirming Israel's defense" and to "send a strong message that we don't want to see any rise in violence, any attacks by Iran or its proxies."
On Monday, a joint statement issued by President Biden and the four European leaders read: "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."
Israel has been preparing for a major attack after Hamas political leader Ismail Haniyeh was killed in Tehran last month, drawing vows of "punishment" from Iran. A day prior, an Israeli strike in Beirut killed a senior commander of Hezbollah.
Israel has neither confirmed nor denied that it was behind the killing of Haniyeh, but the Israeli government had previously pledged to kill him and other top Hamas officials for their role in the group's October 7th terrorist attacks.
US increases military presence in Middle East
Simultaneously, however, the US was rapidly increasing its military presence in the region in anticipation of an Iranian attack.
On Sunday, the Pentagon said that US Defense Secretary Lloyd Austin had ordered the USS Abraham Lincoln, an aircraft carrier equipped with F-35 fighter planes, and its accompanying ships to "accelerate" its deployment to the Persian Gulf. The USS Georgia, a submarine equipped with guided missiles, was also en route.
Also on Monday, German Chancellor Olaf Scholz held a telephone call with the new Iranian President Masoud Pezeshkian in which he emphasized the need for a ceasefire in Gaza and the return of hostages held by Hamas.
"This would be an important contribution to regional de-escalation," Scholz told Pezeshkian, according to a German government statement. "The spiral of violence in the Middle East must now be broken; anything else would pose an incalculable risk to the countries and people in the region."
Israel on 'peak alert,' preparations underway in Haifa
Following Kirby's remarks in Washington, an Israeli military spokesman said Israel was on "peak alert" and taking Iranian threats "seriously" but that there were currently no changes to "home front guidelines" for civilians.
In Haifa, the Israeli port city just 30 kilometers south of the Lebanese border, and therefore well within range of Hezbollah rockets, preparations for an attack by Iran and its allies are already underway.
The city has set up air-raid shelters for tens of thousands of people equipped with generators, Wi-Fi, water reserves and first aid supplies. Some of the shelters, often in converted underground garages, even have nurseries to entertain young children and supplies to last several days.
"We expect a reaction from Iran or Hezbollah and assume something will happen," Haifa's chief catastrophe protection officer Leonid Reznik told the AFP news agency. "They won't remain inactive."
