Eight soldiers have been killed in two roadside-bomb attacks in the south of Thailand.

The first attack late on Thursday occurred in the Ruso district of Narathiwat, one of four southern provinces where an armed  campaign has been raging for years.

The bomb, containing about 20kg of explosives, was buried in a dirt road and detonated by wire, police said.

"The group was on night patrol in a pick-up truck when they were ambushed," Lieutenant Pairat Kiatjaroensiri said.

He said the attackers snatched four guns from the patrol before fleeing.

Three of the five soldiers killed were Muslim and two Buddhist.

Narathiwat, together with the provinces of Pattani and Yala, has a predominantly Muslim population, many of whom have long complained of discrimination, especially in education and job opportunities.

No responsibility claim

In the region's second attack, which occurred on Friday, a bomb buried on a road went off, killing three soldiers in a pickup van, Lieutenant-Colonel Kumpon Ponpakdi said.

Al Jazeera's Wayne Hay, reporting from Yala, where the blast took place, said: "As usual here in southern Thailand, no one has come forward to claim responsibility for the attacks.

"But over the years, much of the violence has been blamed on Muslim insurgent groups who are believed to be fighting for an autonomous region encompassing the three southern provinces of Thailand.

"Officials are also saying that they believe that other organised crime groups are involved in the violence."

More than 4,000 people have been killed in southern Thailand in six years of fighting between security forces and Muslim fighters.

As well as members of the security forces, the fighters usually target people associated with the Thai state, including government officials and teachers.

Tensions have simmered since the region, formerly an autonomous Malay Muslim sultanate, was annexed by predominantly Buddhist Thailand in the early 1900s.

About 90 per cent of those killed are civilians.

The Thai government has made little progress towards quelling the unrest despite deploying thousands of paramilitary troops - usually residents hired as armed auxiliaries to the regular military - in the area alongside 30,000 army troops.

Human rights groups have warned that alleged abuses by the security forces in the region risk further stoking the unrest.