The Middle East braced for another round of violence Monday, after U.S. Secretary of State Antony Blinken said on a call Sunday with Group of Seven foreign ministers that Iran could attack Israel within 24 to 48 hours, according to two diplomats briefed on the call.

Blinken didn’t say what form an attack could take. U.S. officials have been working with their international partners to try to contain tensions in the Middle East amid warnings by Iran and pro-Iranian militias that they will attack Israel following the assassinations last week of Hamas’s political leader, Ismail Haniyeh , in Tehran and senior Hezbollah leader Fuad Shukr in Beirut.

On Monday, Iran called a gathering of foreign diplomats in Tehran. In the meeting, Iranian acting Foreign Minister Ali Bagheri-Kani attacked what he called the complicity of the U.S. and some European countries in supporting Israel, he said afterward on social media.


“Such aggression cannot go unanswered,” he said he told the diplomats. “The Islamic Republic’s response will be definitive and decisive.”

An Arab diplomat said that an Iranian official had said on Monday that an attack could occur “imminently,” within the next 48 hours.

In Washington, President Biden convened his national security team in the Situation Room on Monday afternoon to discuss the crisis in the Middle East, according to the White House. He also spoke with Jordan’s King Abdullah, whose acting foreign minister made a rare visit to Tehran.

The U.S. military was on alert to help defend against any potential attack on Israel in the coming days.

Defense Secretary Lloyd Austin on Friday ordered additional firepower to the region ahead of an expected attack, including an F-22 fighter squadron armed with air-to-air weapons capable of shooting down incoming missiles. With the additional F-22 squadron, there are now several U.S. Air Force squadrons in the region.

Austin also ordered the aircraft-carrier strike group the USS Abraham Lincoln, which is currently in the Pacific, to replace the USS Theodore Roosevelt to maintain a carrier presence in the region.

Gen. Erik Kurilla, head of U.S. Central Command, has flown to the region, as he did in April, and has arrived in Israel, the Israeli military said Monday.

Two destroyers capable of shooting down cruise and ballistic missiles are in the eastern Mediterranean, according to a U.S. official: the USS Bulkeley and the USS Roosevelt. Also in the eastern Mediterranean is the USS Wasp amphibious ready group, in case there is a need for a noncombatant evacuation. The Theodore Roosevelt and its associated strike group are in the Gulf of Oman.

Several U.S. troops were injured Monday in a suspected rocket attack at a U.S. base in Iraq, Pentagon officials said. The U.S. was assessing how many troops at Al Asad air base were injured, the officials said, amid fears that an Iranian proxy group was behind the attack.

The briefing in the Situation Room “focused on the threats posed by Iran and its proxies to Israel and to U.S. servicemembers in the region,’’ the White House said. Also discussed were steps the U.S. is “taking to defend our forces and respond to any attack against our personnel in a manner and place of our choosing.”

On Monday morning, Iran issued a notice to pilots and aviation authorities warning of likely disruption to GPS and navigational signals, which are used by pilots for positional data and to follow flight routes, a U.S. official said. The warning was posted on the website of the U.S. Federal Aviation Administration.

Iran had issued a similar warning on April 13, the day Tehran launched its first-ever direct military attack on Israel .

Iran on Monday afternoon denied reports that it had issued a notice to pilots and aviation authorities regarding flight restrictions or rerouting in its airspace. Iran’s airspace appeared to remain operational with regional flights continuing as of Monday afternoon.

Last week, Jordan issued a notice requiring air traffic coming to its airports to carry 45 minutes of extra fuel.

Iran was seen by some analysts as having telegraphed the April attack before carrying it out, which allowed Israel and its partners time to prepare a response and avoid the sort of damage or casualties that could have sparked a cycle of escalation. Israel waited several days to respond and did so with a targeted strike on an air-defense system in Isfahan that allowed the situation to resolve itself without another strike.

This time could be trickier. Iran has stonewalled efforts by diplomats around the region to get more information about its intentions and encourage it to de-escalate. U.S. officials were on the lookout for indicators such as Iran moving missile launchers into place, as the regime did in April ahead of the missile strike on Israel. And U.S. officials said they had no idea what an attack might look like or the precise time frame.

The U.S. message to Israel is that Washington will act to defend it this time as it did in April, but that Israel needs to show restraint along with its adversaries to preserve the option of a cease-fire in the war in Gaza, which followed the Hamas-led attacks on Israel on Oct. 7.

“We’re preparing to defend Israel in an April-like manner,” a U.S. official said.

Israel’s posture has changed as well, with military leaders saying the country could respond quickly and powerfully to any attack. On Monday, Defense Minister Yoav Gallant said Israel would need to be ready for “a swift transition to offense.”

German flag carrier Lufthansa on Monday said that it had extended the suspension of all flights to Tehran, Tel Aviv and Beirut until Aug. 12 across the group’s airlines. Other carriers, including Delta Air Lines, United Airlines, Air France and Air India have also suspended flights into the region in recent days amid the regional tensions.

Despite a few cancellations, passenger flows were largely normal at Ben Gurion Airport in Tel Aviv. Some travelers said they opted to leave Israel to avoid logistical logjams in the event of an attack.

Jeff Vines, a Christian pastor who lives in Los Angeles, cut his trip short by two weeks. He and his wife, Robin, have traveled twice to Israel to study religious sites and meet leaders of various faiths.

“It was a tough decision, but what we didn’t want was to get stuck,” Vines said.

Others were more concerned about immediate danger. Eliyahu Freedman, a 32-year-old translator and academic researcher, said he had been packing up his belongings for the past two months because he expected the conflict to escalate and his apartment didn’t have a bomb shelter.

The Canadian-Israeli said rhetoric from Israeli and Iranian leaders over the past week convinced him it was time to go. He filled up a backpack with minimal clothes and a few belongings, and booked himself a one-way ticket to Greece.

“It’s really unclear when it’ll be safe to return,” Freedman said. “But I’ve got my yoga mat, some books on meditation and my amulets—anything to try and bring a degree of protection.”

At Beirut’s international airport, Malak Zayno and Hasan Hassan were seeing their daughter off and debating whether to leave Lebanon themselves. “I am scared. I want to leave, but I don’t want to leave him alone,” Zayno said.

Hassan said he was relieved that his children had left. “But I prefer to stay no matter what happens,” he said.

According to one of the diplomats briefed on Sunday’s G-7 call, Blinken told his counterparts that if an Iranian attack on Israel is of a similar scale to April’s attack, it could close off any plans for future engagement between Iran and the U.S., who have held sporadic indirect talks through Omani officials over the last 18 months.

Last week’s killing in Tehran of Haniyeh, who was there to attend the inauguration of Iran’s new president, was an embarrassing security failure for Iran. He was killed by a bomb while staying in an Islamic Revolutionary Guard Corps guesthouse, The Wall Street Journal has reported.

Iran and Hamas, which blame Israel for the attack, disputed that a bomb killed Haniyeh, saying he was struck by a missile. Israel hasn’t publicly commented on the killing.

Write to Laurence Norman at laurence.norman@wsj.com , Benjamin Katz at ben.katz@wsj.com and Feliz Solomon at feliz.solomon@wsj.com