On 11 September 2012, 4 Americans, including visiting United States Ambassador to Libya J. Christopher Stevens, were killed when the U.S. diplomatic mission in Benghazi came under attack. U.S. officials said heavily armed extremists had laid siege to the consulate using "military-style tactics". On 21 September, thousands of demonstrators, along with government police officers, stormed the bases of several Islamist militias in Benghazi, including Ansar al-Sharia, which has been linked to the attack on the U.S. consulate, and forced their members to flee.