Several countries including the United States have issued new travel guidelines for Israel and the surrounding region, as the Israeli military said its forces were “highly alert” for a possible Iranian strike in retaliation for the killings of several commanders.

Iran has repeatedly vowed to strike back at Israel over the bombing of an Iranian Embassy complex in Damascus, Syria, this month that killed three generals and four other military officers. A U.S. official said today that Washington expects an attack by Iran against Israel that would be bigger than recent attacks in the long shadow war between the two countries, but not so big that it would draw the United States into war. The official spoke on condition of anonymity because of the sensitivity of the matter.

The U.S. State Department on Thursday barred its employees from traveling to large parts of Israel, the first time the U.S. government had restricted the movement of its employees in this way since the war in the Gaza Strip began more than six months ago.

On Thursday, Britain told its citizens that they “should consider leaving” Israel and the Palestinian territories “if it is safe to do so.” India told its citizens today “not to travel to Iran or Israel till further notice,” while France advised people not to travel to Israel, Iran or Lebanon and evacuated the families of French diplomats from Iran.

Asked about the U.S. travel warning, Matthew Miller, the State Department spokesperson, said at a news briefing Thursday: “We have seen Iran making public threats against Israel in the past few days.” He declined to provide details about any specific information that prompted the warning.

The new guidelines bar U.S. government employees and their families from traveling to locations outside the Tel Aviv, Jerusalem and Beersheba metropolitan areas of Israel “out of an abundance of caution” until further notice. The State Department said U.S. personnel could move among those areas for personal travel.

The top U.S. military commander for the Middle East, Gen. Michael E. Kurilla, traveled to Israel to coordinate a response to possible Iranian retaliation, U.S. officials said.

“Our enemies think that they will divide Israel and the United States,” Israeli Defense Minister Yoav Gallant said in a statement today after meeting with Kurilla. “They are connecting us and are strengthening the relationship between us.”

If Iran attacks, he added, “we will know how to respond.”

On Thursday, the Israeli military’s chief spokesperson, Rear Adm. Daniel Hagari, said the armed forces were “highly alert and prepared” for any action Iran might take, even as the timing and scale of any response remained unclear. Analysts say Iran, which has long used a network of proxy forces to project power across the Middle East, wants to avoid igniting a full-fledged war that could drag in the United States and threaten the survival of Iran’s regime.

“For years, and even more so during the war, Iran has been financing, directing and arming its proxies — in Lebanon, Gaza, Syria, Iraq and Yemen — to attack the state of Israel,” he said. “An attack from Iranian territory would be clear evidence of Iran’s intentions to escalate the Middle East and stop hiding behind the proxies.”

This article originally appeared in The New York Times.