WASHINGTON - Four American military personnel were detained, then released, in Libya on Friday, the State Department said.

The four were detained by the Libyan government "in an area near Sabratha" in northwestern Libya, near the Tunisian border "as part of security preparedness efforts when they were taken into custody," State Department spokeswoman Jen Psaki said.

The U.S. military personnel were released, the State Dept. confirmed a few hours after initially confirming their detention.

It's unclear what they were doing in the area, but an unnamed U.S. official told The Associated Press that they were investigating potential evacuation routes.

Libya remains volatile, and the State Deptartment has advised Americans to avoid all but essential travel to the Tripoli area and to avoid the rest of the country altogether.

Earlier this month, American teacher Ronnie Smith was shot and killed in Benghazi, where U.S. Ambassador to Libya Chris Stevens was killed in 2012.

Earlier this year, Delta Force member snatched alleged al Qaeda member Anas Al-Libi off the street in Tripoli. He was interrogated on a Navy ship and arraigned in New York City, where he pleaded not guilty of terrorism charges.