The Philippines military, with help from the United States, has spent the past year combing the remote island of Jolo for members of Abu Sayyaf, who work and train with Jemaah Islamiah, Al Qaeda's franchise in Asia.

"We have reasons to suspect the Abu Sayyaf group was behind the latest kidnapping on Jolo island," Ahirum Ajirum, the police chief in Sulu province, told reporters, a day after masked gunmen took away the mother and son who owned a bakery and a pawnshop.

"We heard the gunmen were demanding at least 10 million pesos in exchange for the freedom of Jackylyn and Jeffrey Silbin."

Ajirum said it was the second case of kidnap-for-ransom of local traders on Jolo this year.

The last high-profile abduction of foreign and local tourists in the south happened in May 2001, when Abu Sayyaf beheaded one of three American tourists.

Lieutenant-General Gabriel Habacon, the military commander in the southern Philippines, was more cautious in blaming the Muslim militants for the latest kidnapping.

"We could be seeing a local armed group raising money either for political or cultural purposes," Habacon told reporters in Zamboanga City, a commercial hub in southwestern Philippines.

"We believed the Abu Sayyaf would be going for high-profile targets and stage more spectacular attacks, such as bombings and raids on tourist resorts."