Insurgents open fires on Thai Muslims who were praying in a mosque in Narathiwat on Monday, killing 11 and injuring many others.

It was unclear how many gunmen were involved in the bloodiest incident in the volatile region in months.

Police initially said that a group of about five heavily-armed men broke into Al Pukon Mosque in Joh I Rong district through the back door and sprayed the bullets on about 50 people inside the mosque.

Police said ten of them, including an Imam, died instantly at the scene.

About 12 others were injured.

However, later reports said only two gunmen carried out the attack.

The fatal attack on praying Thai-Muslims was the first of its kind and would deal a major blow on the Abhisit government's efforts to bring peace back to the deep South.

Latest reports also said one of those injured has died, bringing the death toll to 11.

A manhunt has been launched for the attackers. The mosque and surrounding areas have also been sealed off, TV reports said.

"They opened fire indiscriminately at about 50 worshippers inside the mosque,'' a police official said on condition of anonymity, adding that the dead included the local imam or prayer leader.

Army spokesman Colonel Parinya Chaidilok said there were two attackers, one of whom entered through the front door of the building while the other came in by a side door before opening fire.

He confirmed that 10 people were killed instantly and another died on the way to the hospital, while the 12 wounded were all in critical condition.

Parinya said that the identities of the attackers in Monday's incident were not yet known, but that by attacking a mosque they appeared to be carrying a notorious agenda.

"They are trying to make it look like the attackers are the authorities, because Muslims would apparently not shoot inside a mosque. But it's impossible that it is the work of the military,'' he said.

Violence has flared up again in the deep South. Earlier Monday a soldier was killed by a bomb blast and militants shot dead a rubber-tapper. Militants also blew up another army patrol vehicle, wounding nine soldiers.

The mosque attack coincided with Prime Minister Abhisit Vejjajiva's visit to Malaysia, during which the insurgency in the deep South was among topics discussed. Abhisit promised ''justice and opportunities'' for the deep South following talks with Malaysian leaders.

The attack also followed a court verdict late last month acquitting security officials involved in the disastrous Tak Bai protest crackdown in 2004.

The renewed violence occurred as Prime Minister Abhisit Vejjajiva reached out to the survivors of the Tak Bai massacre following the controversial court ruling that cleared security officers involved in the incident.

During his weekly TV address one day before his official visit to Malaysia, Abhisit promised to extend government assistance to the families of the victims.

But he withheld comment on the May 29 decision that absolved security officials of charges of misconduct in the deaths of 85 unarmed Malay Muslim demonstrators five years ago.

The mosque attack was one of the bloodiest for months in the region bordering Malaysia after more than 3,700 people had been killed in the years-long violence in the region.

"This was apparently intended to further divide Thai Buddhists and Thai Muslims in the region," said Maj Gen Theerachai Nakvanich, special task force commander in Narathiwat. "But I don't think whoever did this will achieve their goal because victims are all people in the neighbourhood."

Officials said many of the prayers had come to the mosque from other districts in Narathiwat.