The U.S. issues new travel guidelines, warning that Iran will avenge the killings of senior commanders.

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. An American official said on Friday 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 Gaza 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.” On Friday, India told its citizens “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 spokesman, 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 “out of an abundance of caution” until further notice. The State Department said U.S. personnel could move among those areas for personal travel.