A bomb exploded during Friday prayers at a historic mosque in the southern Indian city of Hyderabad, killing at least seven people, police said.
More than 50 people were injured, including several boys, at Mecca Masjid, the main mosque in Hyderabad, the capital of Andhra Pradesh state.
Thousands of worshippers were praying at the sprawling mosque at the time of the blast.
Officials said the death toll could rise and three other crude bombs were defused as crowds, angered by the attack, clashed with police around the mosque.
"I had just said my prayers and there was a blast. Suddenly I was hit by a rock," Naseeruddin, 45, said as he lay in hospital, his head wrapped in a blood-stained white bandage.
"When I looked up, another rock hit my face. Then I fell unconscious," the street vendor said. Nearby, other wounded men groaned in pain as their relatives kept watch.
New Delhi said it was a "terrorist" attack, but did not name the militant groups under suspicion.
Angry crowds shouting "Allah is Great" fought pitched battles with police around the mosque, pelting stones. Police opened fire in the air after trying to disperse the crowd with tear gas.
Some people hurled stones at shops and vehicles, damaging more than a dozen buses.
A police officer at the scene said the bomb was triggered by a mobile phone.
The blast took place at the area where worshippers wash their hands and face before prayers.