Three people died and some 20 were injured in a clash between Shiites and Sunnis in Lucknow on Sunday.
Curfew was imposed in the area, police said.
Violence erupted at around 11am in Hussainabad as a Moharram procession of Shiites was passing through a Sunni area.
According to the police, a group of Sunnis objected to some recitations being made by Shiites during the procession.
They tried to physically prevent the Shiites from marching through the Sunni-dominated Muftiganj locality of Lucknow.
After some heated exchanges, both sides began to pelt stones at each other. The riot police (Rapid Action Force) could not control the enraged people. The rioters set ablaze parked vehicles and shops.
Three people died in the ensuing melee and may others were injured.
"We have deployed additional force in the area and the situation is now fully under control," Senior Superintendent of Police, Lucknow, Navneet Sikera told reporters.
He said, "The injured have been hospitalised, but none of them are serious."
Lucknow is known for confrontation between the Shias and the Sunnis over the route of the Muharram processions.
However, clashes stopped after an agreement between the two sides in 2000.
A recent decision by the Shias to constitute an All India Shia Personal Law Board independent of what they consider a Sunni dominated All India Muslim Muslim Personal Law Board is supposedly responsible for the bitterness between the two sides.