At least 25 people have been killed in Pakistan's tribal area in clashes over preaching rights between supporters of two rival clerics, officials say.
About 30 others were hurt in the violence in Khyber agency in North West Frontier Province (NWFP).
The rival factions fought pitched gun battles with automatic weapons in the town of Bara, tribal areas spokesman Shah Zaman Khan told news agencies.
Reports say there has been tension between the factions for some months.
The BBC's Zaffar Abbas in Islamabad says the fighting has nothing to do with a security operation against pro-Taleban militants in nearby Waziristan and is more about territorial control and enforcing the conflicting Muslim beliefs of the two rival clerics.
'Tension and fear'
Fighting between the factions began late on Monday after a house was demolished and continued until early on Tuesday, Mr Khan said.
Tribal police assisted by paramilitary troops have been deployed to maintain order.
"The fighting continued the whole night. There is tension and fear in the area," a local resident Sultan Khan Afridi told the Associated Press news agency,
Mohammad Nisar Afridi, a local trade union leader, told the Reuters news agency: "Dead bodies are still lying there and paramilitary troops have sealed off all roads leading to that place."
Hundreds of supporters of Mufti Munir Shakir are reported to have attacked the stronghold of rival Afghan cleric, Pir Saifur Rehman, killing at least 16 people late on Monday, officials say.
Mullah Rehman's supporters are said to have retaliated on Tuesday, attacking their opponents in the nearby town of Bara.
Our correspondent says Mufti Shakir is said to be a hardline fundamentalist who strongly opposes Mullah Rehman's secular Sufi interpretation of Islam.
He says some of the dead are believed to be supporters of the Sufi cleric from Afghanistan.
Bara is the main trade route between Pakistan and Afghanistan and is an important town in Khyber agency which borders Afghanistan. The town is also said to be a hub for smuggled goods.
Both clerics have been operating illegal FM stations to broadcast their religious beliefs and denounce the rival group as heretics.
The two groups have also accused each one another of taking women and children hostage.
Tension has risen sharply in the last few months after an earlier attempt to resolve the dispute through a jirga (tribal assembly) failed.
After an earlier armed clash between the two groups, the security forces intervened to force both the clerics out of the tribal areas.
Although the two clerics have been in hiding since then, their followers continued to fight for control of the territory.