A key member of a leading separatist group in restive southern Thailand was killed in an exchange of fire with security forces on Tuesday, local media reported.

The clash took place on early Tuesday morning after a combined 50-strong military-police force laid siege to a house in Si Sakhon district of Narathiwat province where three or four militants were reported to have been hiding, planning terrorist attacks in the district.

When the authorities showed up, three men slipped out of the house through the back door and one provided covering fire for his colleagues. The two sides exchanged shots for about 10 minutes.

On clearing the scene, the security team found a man lying dead holding a .38 pistol in one hand in the rubber plantation behind the house, Bangkok Post online reported, adding that the others escaped.

The dead man was later identified as Sofh Torueno, 40, resident of Narathiwat's Ruso district. He was a core member of Runda Kumpulan Kecil -- an active local terrorist threat in Southern Thailand -- wanted under warrants for more than 10 cases of violence in three districts from 2004 to 2010.

The authorities seized from the scene one .38 pistol with 10 rounds of ammunition and one motorcycle.

A suspected supporter of the militants was taken for questioning.

More than 5,000 people have been killed and over 8,400 hurt in the three southernmost provinces of Yala, Pattani and Narathiwat, since violence erupted in January 2004, according to Deep South Watch -- an agency that monitors the conflict in the southernmost provinces.