Three alleged members of al-Qaeda killed in latest attack in Shabwah province, according to tribal and military sources.
The United States has said it will close an unspecified number of embassies around the world on Sunday over security concerns.
State department spokeswoman Marie Harf on Thursday called the step “precautionary” but declined to specify the threat or list which missions would be closed.
But a senior state department official later told reporters they were those that would normally have been open on Sunday, including several US missions in predominantly Muslim countries such as Egypt and Iraq.
“The Department of State has instructed certain US embassies and consulates to remain closed or to suspend operations on Sunday, August 4,” Harf told reporters.
The decision was taken “out of an abundance of caution and care for our employees and others who may be visiting our installations,” she said.
Harf said that the embassies would be closed specifically on Sunday, with an assessment afterwards on whether to reopen them.
“It is possible we may have additional days of closing as well,” she said.
Harf declined to specify from which part of the world the threat was detected.
Government offices are nearly always closed in the US on Sunday, which is the start of the work week in many Muslim-majority countries.
The US has been especially cautious about security since an attack on its consulate in Benghazi, Libya on September 11 last year.
The attack killed four Americans, including ambassador Chris Stevens, and led critics in Congress to accuse the state department of insufficient security.