Four American military personnel working on security preparedness operations in Libya were detained Friday and released after being taken into custody by the government, the State Department said. "We are still trying to ascertain the facts of the incident,” said spokesman Jen Psaki. The four were supporting US Marine security forces protecting the American Embassy, the official said. They were likely US special operations forces, which have been deployed to Libya. Tensions have run high between the United States and Libya since a terrorist attack against the US consulate in Benghazi on Sept. 11, 2012 resulted in the deaths of four Americans, including Ambassador Christopher Stevens.