Zamboanga City, Philippines - Three people were killed and seven wounded Monday when gunmen attacked a truck owned by a rubber plantation cooperative in the southern Philippines, police said.

The ambush occurred in Lantawan town in Basilan province, 900 kilometres south of Manila, said Senior Superintendent Salik Macapantar, provincial police commander.

Macapantar said four of the wounded were in critical condition and rushed to hospital in Isabela City.

He said police still have no suspects and were investigating the ambush.

Security has been heightened in Basilan as government troops hunt down Muslim Abu Sayyaf rebels holding captive six teachers, a Sri Lankan peace advocate and a lending firm employee.

Last week, the al-Qaeda-linked guerrillas released a 9-year-old boy after the family paid an undetermined amount of ransom.

A separate group of Abu Sayyaf rebels are holding captive two European Red Cross workers on the nearby island of Jolo.

The guerrillas freed a third Red Cross captive last week but threatened to kill the remaining hostages if government forces do not pull out from a large area of the island. (dpa)