At least three died in police firing during protest against a Facebook post that allegedly insulted Prophet Muhammad.
Baton-wielding police have patrolled barricaded and deserted streets in parts of the southern Indian tech hub of Bengaluru, after three people were killed in Tuesday night clashes triggered by a Facebook post offensive to Muslims.
A police official said an emergency law prohibiting gatherings had been imposed in Bengaluru, a city of 12 million people known as India's Silicon Valley.
The violence began late on Tuesday, with mobs pelting stones, burning vehicles and setting a police station on fire, and lasted until the early hours of Wednesday. Dozens of people were wounded.
"Seeing that much fire, smoke and the violence was really scary. I was really frightened. We've only seen such things on TV," said Ahan Khan, a college student who lives near the police station in northeast Bengaluru.
Police said the person responsible for the offensive post, which has since been deleted, had been arrested. A spokesman for Facebook said it was investigating, adding its standards prohibit hate speech and incitement to violence.
The state government headed by the Bharatiya Janata Party (BJP) on Wednesday ordered an investigation into the worst violence in the city in more than 20 years.
Bengaluru Police Commissioner Kamal Pant said his officers had initially tried to hold back around 1,000 protesters using batons and tear gas, but then opened fire.
"The police had no escape and they had to resort to firing and three people died," Pant said, adding that 110 people had been arrested for alleged vandalism and attacking the police.
The three victims were Muslim men aged between 19 and 21, said Rizwan Arshad, a Congress party legislator in Bengaluru, who reached the police station amid the violence on Tuesday night to appeal for calm.
A medical officer at the government-run Bowring hospital said they had treated at least 27 injured policemen and 12 protesters, including three who had suffered gunshot wounds.
Police gave the first name of the accused man as Naveen, and said he was the nephew of a Congress politician, whose house was attacked and burned in the violence.
The politician, R Akhanda Srinivasa Murthy, appealed for calm in a video message carried by media.
"We're all brothers. Whatever crime has been committed, let the law teach them a lesson," Murthy said. "I appeal to our Muslim brothers and everyone else to maintain peace."
Television channels on Tuesday night showed a group of people gathered outside a police station, clashing with officers and burning several police vehicles.
On Wednesday afternoon, charred remains of several cars and motorcycles were strewn across the basement car park of DJ Halli police station, the facade of which was also scarred by fire.
Nearby streets were lined with burned vehicles, with all shops shuttered along the nearly two kilometre-stretch where the police station is located.
"We are investigating the issue and will make use of the CCTV footage to see who is behind these violent acts, and will take stringent actions," said Basavraj Bommai, home minister of Karnataka state, where Bengaluru is located.
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