(Adds details, background) BANGKOK, May 9 (Reuters) - A roadside bomb attack killed seven soldiers in a pick-up truck in Muslim-majority southern Thailand on Wednesday, one of the single deadliest attacks in three years of separatist unrest, army and police officers said. The bomb, which exploded in Narathiwat -- one of the three southernmost provinces where more than 2,100 people have been killed -- demolished the vehicle, army spokesman Colonel Acra Tiproch told Reuters, citing an initial field report. "The improvised bomb weighed about 15 kg (33 lb) and was stashed in a fire extinguisher placed in a roadside ditch," said Sompong Tangtua, a police lieutenant-colonel at the scene. The bomb was detonated by a wire strung across the road and some soldiers who appeared to have survived the initial blast were shot dead, he said. Their weapons were taken. In a separate incident in the region, an independent sultanate until it was annexed by mainly Buddhist Thailand a century ago, police said a Muslim man was shot dead as he rode his motorcycle in neighbouring Yala province. His 12-year-old son, also on the motorbike, was wounded. Thailand's army-backed government said last week it was considering a limited amnesty for those suspected of involvement in the insurgency, which international security experts fear could attract the likes of Osama bin Laden's al Qaeda. However, the amnesty offer appears to be making no difference to the militant movement, which has never gone public with its aims. Around 80 percent of people in the far south are Malay-speaking Muslims and have few connections to the rest of the nation of 65 million people. Around 500 Muslims have held rallies and blocked roads in Yala in the past week demanding the government release 21 Muslims detained on suspicion of links to the unrest. Prime Minister Surayud Chulanont, appointed after a September military coup against elected Prime Minister Thaksin Shinawatra, is due to travel to the region on Sunday.
