Two bombs exploded minutes apart in a packed Istanbul square Sunday night, killing 16 and injuring more than 150 in the deadliest attack against civilians in Turkey in almost five years. The city's governor called it a "terror attack" but officials did not blame any specific group and no one immediately claimed responsibility. CNN-Turk television, citing security sources, said police suspect Kurdish rebels may be behind it because intelligence reports had suggested the rebels were planning a bombing campaign in Turkish cities. "There is no doubt that this is a terror attack," Gov. Muammer Guler told reporters. The first bomb went off in the residential neighborhood of Gungoren in a busy square closed to traffic where people congregate at night, witnesses said. A number of people had rushed over to see what happened and help the victims when a second, more powerful blast hit close by about 10 minutes after the first. Many of the casualties were from the second explosion, witnesses said.