Pattani, Thailand - A Royal Thai Army helicopter crashed Friday while searching for Muslim separatists in the conflict-ridden deep South, killing all 10 people on board, an Army spokesman said.

The helicopter crashed into a hillside in the Bannang Sata district of Yala province, 780 kilometres south of Bangkok, while searching for insurgents who had attacked an Army patrol in the area earlier Friday, leaving one soldier dead and three wounded, said Southern Army Region spokesman Colonel Arca Tiproch.

"The engine failed and the helicopter crashed into a hillside at high speed," Arca said, adding that three people survived the crash. Meanwhile, in nearby Narathiwat province, a roadside bomb injured five soldiers on patrol.

They were the latest incidents to rock Thailand's deep South, a majority-Muslim region comprising Narathiwat, Pattani and Yala provinces, which border Malaysia. An estimated 2,700 people have died from an increasingly bloody separatist struggle in the region over the past three and a half years.

More than 80 per cent of the three provinces' 2 million people are Muslims, making the region an anomaly in predominantly Buddhist Thailand.

A separatist struggle has simmered in the area for decades, but took a turn for the worse in January 2004 when Muslim militants attacked an Army depot and stole 300 weapons, prompting a crackdown that further inflamed the local population against the government. (dpa)