The circumstances in which the four were taken into custody were unclear, the New York Times reported. The newspaper said it appears to have happened in a town about an hour from Tripoli by vehicle in an area believed to be pro-Western, and U.S. officials said the four were assigned to the U.S. Embassy in Tripoli and were scouting possible evacuation routes.
"We are seeking to further ascertain the facts and ensure their release," Jen Psaki, a spokeswoman for the department, said. "We are in touch with Libyan officials on this issue."
Since J. Christopher Stephens, the U.S. ambassador to Libya, and three members of his security team were killed in September 2012 in an attack on the consulate in Benghazi, U.S. diplomats in Libya have operated under tight security. They live and work in a guarded compound, venturing outside only with armed guards on trips planned in advance.