The first American service members to die in the U.S.-Israeli war with Iran were killed in an apparent Iranian drone attack on a makeshift office space in Kuwait, sources told CBS News.

Photos show US pilot being rescued after apparently ejecting over Kuwait - as smoke seen rising near the US embassy

As the war between the United States and Iran enters its third day, the death toll of American servicemen continues to climb, now reaching six deaths.

The U.S. State Department closed embassies in Kuwait and Saudi Arabia on Tuesday and is urging Americans to evacuate from 14 Middle Eastern countries as the war with Iran escalates.

The first US service members to die in the conflict between the US and Iran were killed by a direct Iranian strike on a makeshift operations center at a civilian port in Kuwait on Sunday morning

In its advisory, the department said personnel in Jordan and Bahrain face continuing risks from potential Iranian drone and missile attacks, along with disruptions to commercial air travel and the possibility of terrorist activity. In Iraq, officials warned of elevated dangers including violence and kidnapping.

Iran and Iranian-backed militias fired missiles at Israel and Arab states, apparently hitting the U.S. Embassy compound in Kuwait, while Israel and the United States pounded targets in Iran on Monday.

Kuwait’s Ministry of Defense said “several United States military aircraft crashed” on Monday and that “all crew members survived.”