The State Department issued a travel warning on Sunday and is allowing family members of U.S. Embassy staff and non-essential personnel to leave Yemen as violence escalates.
The advisory stated that in the event of a crisis, evacuation options would be severely limited due to "the lack of infrastructure, geographic constraints, and other security concerns."
The State Department said the threat level in Yemen, where demonstrators are calling on the country's besieged president to leave office, is "extremely high."
"Piracy in the Red Sea, Gulf of Aden and Indian Ocean is also a security threat to maritime activities in the region," the travel warning said.
The State Department also said the U.S. government has continued concerns about possible attacks against American citizens, facilities and businesses.
Suspected al Qaeda fighters ambushed and killed four Yemeni soldiers on Sunday who were distributing food to other troops manning checkpoints in a remote, mountainous region of the country.