Bomb explosion rocks crowded street in central Istanbul

A bomb blast in Istanbul has killed at least six people and wounded dozens more. The explosion ripped through a cowded pedestrian street near Taksim Square in the city center. Turkey's President Recep Tayyip Erdogan says the attack appears to be terrorism - and has vowed to punish the bombers. No group has yet said it was behind the explosion. Groups including Kurdish separatists and Islamist militants have previously targeted Istanbul and other Turkish cities.