Troops killed four suspected insurgents during a gunfight in Thailand's restive Muslim southernmost provinces, the military said Monday, the latest unrest in a region plagued by years of separatist violence.

The four men were shot dead late Sunday and three others wounded when a gunbattle broke out during an inspection of a pickup truck by soldiers manning a checkpoint in Pattani province, 1055 km south of Bangkok.

As troops approached the truck, a pair of unknown gunmen appeared from behind the vehicle and opened fire before fleeing on a motorcycle, said Akara Thiproj, the regional army spokesman said.

The four suspected insurgents who were killed were in the back of the truck. An assault rifle was also found there.

This is an area that has been under a lot of insurgent influence. There were similar attacks on military officers in this area in the past, he added.

Relatives of the victims and residents of their villages gathered Monday and voiced their anger at the military for what they said were unlawful shootings, claiming a cover-up and insisting those killed were not insurgents.

More than 5,000 people have been killed since a shadowy, decades-old separatist insurgency resurfaced in January 2004 in Yala, Pattani and Narathiwat provinces bordering Malaysia.

The tens of thousands of police and troops based in the region have made little progressing in tackling the near daily shootings and bombings, for which no credible group has publically claimed responsibility for.

The region was part of an ethnic Malay Muslim sultanate before it was annexed by predominantly Buddhist Thailand in 1909 and tensions have simmered ever since, with resentment running deep among local Muslims about the presence and conduct of the security forces.

(Reporting by Surapan Boonthanom in Yala and Sinsiri Tiwutanond in Bangkok; Writing by Martin Petty; Editing by Sanjeev Miglani)