As Hizbollah on Friday seized control of western parts of Beirut, the Lebanese capital, Arab and western officials embarked on a flurry of activity amid fears that the conflict could grow into a wider regional crisis.

A US official said the pro-western government was being undermined by the “criminal acts of an illegitimate armed gang”, in reference to Hizbollah, while the weak Lebanese administration accused the Shia militant group of conducting a coup d’état.