ISTANBUL — An explosion on Istanbul’s popular pedestrian Istiklal Avenue Sunday has left people dead and injured, a senior official said. Istanbul Gov. Ali Yerlikaya tweeted that the explosion occurred at about 4:20 p.m. (1320 GMT) and that there were deaths and injuries, but he did not say how many. The cause of the explosion was not clear. A video posted online showed flames erupting and a loud bang, as pedestrians turned and ran away. Other footage showed ambulances, fire trucks and police at the scene. Social media users said shops were shuttered and the avenue closed down. Broadcaster CNN Turk said 11 people were injured. The avenue is a crowded thoroughfare popular with tourists and locals, lined by shops and restaurants. Turkey was hit by a string of deadly bombings between 2015 and 2017 by the Islamic State group and outlawed Kurdish groups.