CAIRO — A militia in Benghazi, Libya, tied to the killing of Ambassador J. Christopher Stevens fled its headquarters on Monday after an hourslong gun battle with a local military unit, a potential turning point in a continuing struggle between Islamists and their foes for control of the city. Libyan army troops during clashes with Ansar al-Shariah, a local hard-line Islamist group, on Monday in Benghazi. At least nine people were killed and more than 50 were wounded, health officials said, as the battle flared out across Benghazi, beginning before dawn. Stores and schools were closed. The local authorities advised...