Insurgents kept security authorities running in Pattani Sunday with a string of up to 50 coordinated bombing and arson attacks.

They included a bomb blast outside a restaurant in Pattani town about midday which killed three defence volunteers. The bomb was hidden in a pile of clothes outside the restaurant. The blast also injured dozens of people.

The blast was part of a spate of coordinated attacks by separatist militants in Pattani's Muang and Yaring districts which started at 6pm on Saturday.

Authorities believe the militants intended to create unrest by detonating bombs at various locations in the hope of sparking chaos.

The deadly explosion took place just before noon outside a three-storey restaurant near the clock tower circle in the municipal area.

Two defence volunteers, Wirot Janthasiri and Sukree Duereh, were killed on the spot. The third victim, Itthipol Ahsae, was pronounced dead at hospital. The explosion also damaged a car and 10 motorcycles.

Authorities said two bombs were set to go off. One was detonated but was not fully functional. Both bombs, weighing 10kg each, were hidden inside fire extinguisher canisters.

About an hour later, a bomb was found near a fire-gutted Diana supermarket and successfully defused before it went off.

The supermarket, located on Udom Vithi Road, was damaged 12 hours earlier in a blaze which was triggered by a firebomb explosion. No one was injured.

Another explosive device was discovered at 6.40pm on Saturday outside Paisal shop on Udom Vithi Road. It was set to go off shortly before midnight.

This device went off about 7pm near a karaoke bar on Ramkomut Road, injuring one person. It was not fully functional.

A third device, a motorcycle loaded with a 50kg bomb, was successfully defused. Police collected fingerprints for examination.

Two firebombs were found and defused at two different shops before Diana supermarket was set ablaze.

As the firefighters battled with the blaze, a fire broke out at a four-storey electrical appliance store. An elderly couple was rescued.

Simultaneously, a firebomb exploded at a cooking ware store on Suwan Mongkol Road. The shop owner was quick to put out the fire.

A defence volunteer shelter, a mobile telephone signal tower and closed-circuit television cameras were set on fire in three arson attacks in Yarang district Sunday morning, as the spate of attacks continued.

The first fire in Yaring was reported about 3.30am when the living quarters of the village defence team of Ban Pulato Rayo was set alight with the attackers using motorcycle tyres soaked with petrol.

At the same time, a mobile telephone signal tower at Ban Posan was torched with old motorcycle tyres. The damage was estimated at 8 million baht.

Five closed-circuit cameras at three locations were burned down, including the one in front of Yarang Hospital.

Pitak Korkiatpitak, mayor of Pattani's Muang district, said he was reluctant to link the weekend attacks with the deaths of 16 militants in Narathiwat last week. "The insurgents strike whenever they see a chance. We have to step up security and surveillance," he said.

About 50 heavily armed gunmen stormed a military base in Narathiwat on Wednesday but were repelled in a counter-attack which killed 16 assailants.

Some observers believed the militants would stir up more violence to avenge the deaths of their colleagues.

Police said potential suspects were filmed by surveillance cameras in four spots.

They were apparently new recruits working under rebel leader Masorreh Duerameh.

Pattani police chief Pol Maj Gen Ekkaphob Prasitwattanachai insisted Sunday surveillance was not lax.

"We've placed the town under surveillance as intelligence estimates suggest there were 50 coordinated attacks. We managed to prevent attacks in eight spots," he said.

The atmosphere in Muang district was grim. Most businesses were closed and people stayed indoors.

Bomb disposal squads, fire trucks and ambulances were on standby and checkpoints sprang up every 300 metres across the town to screen vehicles and people.

Narathiwat, Yala and five districts of Songkhla were placed on the highest security alert following the Pattani violence.