PATTANI, Thailand, Dec 4 (Reuters) - A motorcycle bomb exploded outside a busy restaurant in Thailand's rebellious Muslim south on Tuesday, killing six people, including two boys, government officials said. Two Muslim men died instantly when the bomb, left in a motorcycle parked in front of the restaurant, exploded in Pattani, one of four southern provinces where more than 2,600 have been killed in nearly four years of insurgency, an army spokesman said. "We suspect the two dead men might have been the bombers who failed to escape before the bomb exploded," Acra Tiproch said by telephone from the Muslim south. Two women and two boys died at the hospital where 25 wounded people were being treated, Pattani's deputy governor Vinai Kruvanapat told reporters at the hospital. The southern violence is centred in the region bordering Malaysia, a Malay-speaking former sultanate annexed by Thailand about a century ago. Since July, security forces have launched almost daily raids on suspected insurgent hideouts in villages and towns and have detained dozens of people without charge. Human rights groups say detainees are exposed to potential abuses by the army, which is operating under martial law that grants soldiers immunity from prosecution. (Reporting by Khemin Guagoon; Writing by Nopporn Wong-Anan; Editing by Martin Petty and Alex Richardson)