NEW DELHI  A series of apparently synchronized explosions tore through four towns in the troubled state of Assam in northeastern India on Thursday, killing at least 74 people and leaving about 350 wounded, according to witnesses and the police.

The bombs were aimed at crowded markets and government buildings like courts and police stations, witnesses said. The attacks, among the bloodiest in recent months, left streets littered with bodies and the wreckage of cars and motorcycles, according to witnesses and photographers at the scene.

There were no immediate reports that any group had taken responsibility for the bombings.

For many years, Assam State has been riven by a separatist insurgency led by the United Liberation Front of Assam, which demands independence for this region of some 26 million people and is often blamed by the authorities for bombings. Last month, ethnic clashes left 57 people dead in the area when indigenous Bodos fought with Bengali-speaking Muslims.

According to witnesses and the police, at least nine blasts rocked the four towns attacked on Thursday, including three in the state capital, Guwahati. One of the bombs there had been left in the parking lot of the district court.