Manila - Muslim militants holding captive three staff of the International Committee of the Red Cross (ICRC) on a southern Philippine island have been evading pursuing troops by constantly moving their hostages, a police official said Monday.

Director General Jesus Verzosa, national police chief, said government security forces were having a difficult time pinpointing the exact location of the kidnappers on Jolo island, 1,000 kilometres south of Manila.

"It's the normal move of any kidnap group to (be mobile) to avoid detection," he said. "We have yet to trace their exact location."

It has been almost two weeks since Swiss Andreas Notter, Italian Eugenio Vagni and Filipino Mary Jean Lacaba were abducted after visiting the provincial jail on Jolo.

Police said gunmen led by a sacked jail guard seized the three ICRC staff and then turned them over to al-Qaeda-linked Abu Sayyaf rebels in the jungles of Indanan town.

Verzosa said the police were working closely with the military and a task force headed by the governor of Sulu province, which includes Jolo island, in efforts to recover the hostages. But he declined to give details to avoid jeopardising operations.

"Our anti-kidnap operations are continuing," he said. "We are (undertaking) efforts as in other kidnap-for-ransom situations and the operational matters should not be discussed because our primary concern is the safety of the hostages."

Defence Secretary Gilberto Teodoro added that troops have stepped up security on Jolo in anticipation of attacks by Abu Sayyaf rebels to divert military attention.

"The military has tightened checkpoints around Jolo because the kidnappers might launch divertionary tactics," he said.

According to military intelligence sources, Abu Sayyaf commanders Albader Parad and Akmad Jumdail were leading a group of about 30 men in holding the hostages.

The sources added that the kidnappers were planning to seek 5 million dollars in ransom and unknown political demands for the safe release of the hostages.

Authorities have declined to confirm the reports. The ICRC said it has not received a ransom demand.

The Abu Sayyaf has been blamed for some of the worst terrorist attacks in the Philippines.

It is also notorious for high-profile kidnapping-for-ransom cases, including the abduction of 21 European tourists and Asian workers from a Malaysian resort island in 2000. The hostages were ransomed off for millions of dollars before they were freed months later. (dpa)