At least 40 people have been killed and dozens wounded in two days of clashes between Sunni and Shia Muslims in north-western Pakistan
Fighting erupted after gunmen fired on Shias in Parachinar, about 250km (150 miles) south-west of Peshawar, in North West Frontier province, reports say.
Authorities imposed a curfew on the town and sent troops to restore order.
Sectarian violence has plagued Pakistan for years with Parachinar suffering a number of Sunni-Shia clashes.
Last year a dispute over a shrine left about 20 people dead.
The violence on Saturday prompted officials to issue orders to shoot on sight any person violating the curfew.
At least 14 of the dead were killed when rockets hit their home early on Saturday, officials said.
Sahibzada Mohammad Anis, a senior official in the semi-autonomous Kurram tribal region, told Reuters news agency both sides were using heavy weapons in the clashes.
He said government helicopter gunships had fired at rivals' positions and would do so again if the fighting did not cease.
The trouble started on Friday when Shias protested outside their mosque against Sunnis who had allegedly chanted anti-Shia slogans.
Resulting gunfire directed at Shias by unidentified attackers led to raids on Sunni businesses and homes.
Local Sunni leader Shirin Mengal said about 400 Sunni homes and shops had been burned.
"I appeal to the government to send more troops to Parachinar to avoid any further casualties," he said.
Officials said residents also attacked soldiers.
Minority Shias make up about 15% of Pakistan's population of 160m.
The secretary for law and order in the semi-autonomous tribal region, Arbab Mohammed Arif Khan, said he was asking clerics from both sects to try to control the situation.
The Sunni-Shia schism dates to a 7th Century dispute over the heir to the Prophet Mohammad.
Pakistan: 40 Die in Sunni-Shiite Clashes