NARATHIWAT: Five people, including three military rangers, were killed in a bomb attack in Thailand`s troubled Muslim-majority southern provinces, police said Friday.

The roadside blast ripped though the rangers` truck late Thursday while they were on patrol in Ruso district in Narathiwat, one of three insurgency-plagued provinces near the Malaysian border.

A security volunteer and a deputy village headman also travelling in the vehicle were killed in the attack by suspected Islamist separatists, police said.

The bomb, containing about 20 kilos (45 pounds) of explosives, was buried in a dirt road and detonated by wire. After the blast, the attackers moved in with guns to ensure the victims were dead, police said.

The attackers then seized four assault rifles and fled the scene.

More than 4,100 people -- both Buddhists and Muslims -- have been killed in six years of attacks led by a shadowy mix of Islamist and separatist militants.

The Muslim-majority region was an autonomous Malay Muslim sultanate until it was annexed in 1902 by mainly Buddhist Thailand and tensions have simmered there ever since, flaring up into the current insurgency in January 2004.

Successive governments have struggled to contain the unrest in the southern provinces, where emergency rule has been imposed for nearly five years.

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

According to New York-based Human Rights Watch, separatist militants appear to have stepped up their attacks in retaliation for the death in "suspicious circumstances" of a 25-year-old suspected insurgent in May.

BDST: 10:11 HRS, July 2, 2010