The U.S. Embassy in Yemen closed its doors to the public Saturday for security reasons after the State Department warned Americans not to travel to this Arab country, diplomats said Saturday. Embassy spokesman John Balian did not elaborate on the security concern nor say how long the closure would last. On Friday, the State Department said the security threat to U.S. citizens "remains high due to terrorist activities" and authorized the voluntary departure of non-emergency personnel and eligible family members. It also advised U.S. citizens to avoid unnecessary travel to Yemen. The State Department said it was concerned that extremists might carry out attacks against U.S. citizens or interests and that the embassy may temporarily close or suspend public services occasionally for security reasons. The British Embassy also closed to the public Saturday citing security reasons.