Marines in Yemen and the surrounding region remain at the ready to There were no new movements by Marine forces to bolster security at the U.S. eEmbassy there — or even evacuate personnel, if needed — as rebels seized the presidential palace Tuesday morning in the capital of Sanaa.

Yemen's U.S.-backed leadership came under serious threat Monday as government troops clashed with Shiite rebels near the presidential palace and a key military base in what one official called "a step toward a coup." The same day, a State Department vehicle carrying U.S. diplomatic personnel was also shot at, CNN reported. The vehicle was at a checkpoint near the embassy, and there were no injuries, according to CNN.

There are no immediate plans to evacuate the embassy amid the rising tensions in Sanaa, according to a State Department official. A contingent of Marines with Special Purpose Marine Air-Ground Task Force-Crisis Response-Central Command have been augmenting security at the embassy for months, a Defense Department official said. The unit was stood up in the fall and is based in several locations in the CENTCOM area of operations.

Also in the region is the 24th Marine Expeditionary Unit, currently afloat in the Gulf of Aden off the Yemeni coast. So far, the unit has made no additional movements in response to escalating violence, according to the State Department official.

The crisis response Marines aren't the first to bolster security at the U.S. Embassy in Yemen. West Coast rifle companiesy's — including 100 members of India Company, 3rd Battalion, 4th Marines out of Twentynine Palms, California, and Bravo Company, 1st Battalion, 1st Marines outr of Camp Pendleton, California — have deployed to Sanaa for similar missions since 2013.

The U.S. Embassy in Yemen regularly sees protests, including demonstrations that sometimes turn disruptive and dangerous. In late September, an al-Qaida splinter group fired a rocket attack at the U.S. Embassy there, and State Department officials warn that Americans traveling or living there might be targeted.

"The U.S. Department of State warns U.S. citizens of the high security threat level in Yemen due to terrorist activities and civil unrest," reads the latest State Department travel advisory for Yemen, published in September. "The Department urges U.S. citizens to defer travel to Yemen and those U.S. citizens currently living in Yemen to depart.

"The security threat level in Yemen is extremely high. The Embassy is subject to frequent unannounced closures. In May 2014, the Embassy was closed for almost five weeks because of heightened security threats."

Staff writer Joshua Stewart and The Associated Press contributed to this report.