NBC News reported that the reinforcements were sent to Israel, Turkey and Jordan, citing five defense officials.
The deployment comes as Israeli troops opened fire alongside a border fence between Israel and the Gaza Strip, killing at least 52 Palestinians and wounding 2,400 others, according to the Gaza Health Ministry. It marked the bloodiest day in Gaza since a seven-week Israeli operation against Hamas, which controls the territory, in summer 2014 after the abduction and killing of three Israeli teenagers by the militant group.
Alvis said the Marines are members of the Marine Security Guard Security Augmentation Unit (MSAU), headquartered at Quantico, Va., and created in response to the deadly attacks on U.S. diplomatic and intelligence facilities in Benghazi, Libya, in 2012. Marines who are part of the unit have previously served as embassy security guards and typically deploy for about 45 days at a time, according to a Marine Corps briefing.
The Marines also maintain Fleet Anti-terrorism Security Teams (FAST), which deploy in times of crisis at embassies to reinforce them. Augmentation teams are typically deployed before a situation has mushroomed into a crisis.
The State Department issued several security alerts in the region in recent days, and last week it prohibited U.S. government employees from traveling to the Golan Heights, a section of Syria that is occupied by Israel.
Loveday Morris contributed to this report.