India ? Bombs planted in cars and rickshaws ripped through crowded markets in a coordinated attack Thursday in India’s volatile northeast, killing at least 76 people and wounding more than 300.

The scale and planning behind the 13 blasts surprised authorities, who struggled to determine who was behind the attacks – among the worst in a region plagued by separatism, ethnic violence and Islamic militants.

Seventy-six people were killed, with more than a dozen dying from their injuries overnight Thursday, said Subhash Das, a senior official in the state’s Home Ministry, today.