The military is negotiating their release with the Southern Movement, a secessionist group that wants independence for the south, the official said. He spoke on condition of anonymity because he was not authorized to talk to reporters.
He said the foreigners were taken as they were driving from the province of Lahj to the port city of Aden.
One of those seized is a French citizen of Moroccan descent, according to the official. He said she worked for the U.N. High Commissioner for Refugees, helping refugees who have fled fighting between al-Qaida and government forces.
The French Foreign Ministry and the International Committee of the Red Cross declined to comment. The refugee agency did not return calls for comment after office hours Tuesday.
Security in Yemen has unraveled in recent months during an uprising against the 30-year reign of President Ali Abdullah Saleh. The situation is particularly bad in the south, where al-Qaida-linked militants have taken control of entire towns.
Three French aidworkers held by militants there for six months returned home last week.