Five people, including two policemen, were killed in clashes between Hindus and Muslims on Monday in Haryana state bordering the capital New Delhi, police officials said.
The clashes occurred as a Hindu religious procession passed through the Muslim-majority Nuh region.
District police spokesman Krishan Kumar said: "The procession was supposed to move from one temple to another, but clashes broke out on the road between the two sides, killing 4 people."
He said two of the dead were members of a volunteer guard force helping police control civil unrest.
Another 10 police officers were injured in the clashes, he said.
By Monday evening, the violence had spread to the nearby city of Gurogram, where a mosque was set on fire around midnight, killing one person and injuring another.
Prohibition orders have already been issued in the area after some cars were set on fire yesterday evening, and schools and universities were ordered to close on Tuesday.
"The attackers (who set fire to the mosque) have been identified and a number of them have been arrested," police said in a statement on Tuesday morning, adding that security around places of worship had also been tightened.