At least 13 people have been killed in a bomb explosion at a historic mosque and subsequent rioting in the southern Indian city of Hyderabad, police said.
Many of the injured are in a serious condition
At least nine people were killed and dozens more hurt in the blast during Friday prayers at the Mecca Masjid, one of India's biggest mosques.
Several more people were killed when police opened fire on a crowd of protesters near the mosque.
Police said they also found and defused two homemade bombs near the mosque.
Interior Minister Shivraj Patil said the explosion at the entrance to the mosque was caused by a "crude bomb".
It is not clear who carried out the attack.
The BBC's Omer Farooq, in Hyderabad, says police have sealed off the area around the mosque but there are reports of clashes between both rival groups and police and protesters elsewhere in the city.
Prime Minister Manmohan Singh condemned the attack and urged citizens "to maintain peace and communal harmony".
YS Rajashekhar Reddy, chief minister of Andhra Pradesh state, of which Hyderabad is capital, said the bombing was an act of "sabotage on the peace and tranquillity in the country".
The blast took place as thousands of Muslims were ending Friday prayers at the Mecca Masjid.
Hyderabad is one of the biggest cities in southern India and has a large Muslim population, many of whom live in the congested old city where the mosque is located.
There was chaos and anger after the explosion. Many in the congregation ran for cover, some covered in blood. Ambulances ferried the injured to hospital.
"I was very close to the spot of the blast," one man, Abdul Quader, who escaped with minor leg injuries, told the Associated Press news agency.
The area near the mosque was left strewn with personal possessions
"As soon as prayers ended, we were about to get up, there was a huge deafening blast sending bodies into the air," he said.
"People started running helter-skelter, there was such confusion. People were bleeding, running around in a very bad condition."
Crowds angered by what they said was police failure to protect them gathered and began throwing stones at riot police, who responded with tear gas.
Some reports say police fired live ammunition at the protesters.
Several people were killed in the clashes, officials say.
There are fears that the number of dead from the bombing could rise further. Police say some of the injured are in a serious condition.
Last year more than 35 people were killed after bomb attacks near a mosque in the western state of Maharashtra. It is still not clear who carried out those attacks.