Manila /Geneva - The Red Cross on Monday issued an emotional plea for the lives of its staff members being held hostage by Abu Sayyaf rebels in the Philippines who threatened to behead one of the aid workers.

"Our message to Abu Sayyaf is: Please spare and release Mary Jean, Eugenio and Andreas," Jakob Kellenberger, the president of the Geneva-based International Committee of the Red Cross (ICRC) said in a statement.

Mary Jean Lacaba, Eugenio Vagni and Andreas Notter, humanitarian aid workers with the ICRC, have been held captive since January 15, when they went to the field to conduct water and sanitation projects.

They were being held on Jolo island, 1,000 kilometres south of Manila, the capital. The rebels threatened to kill one on Tuesday if their demands, including the withdrawal of government forces, were not met, according to officials.

"All they were doing was helping people in need in your area. There is no ideology or religious law that could justify killing them," Kellenberger said, pledging to do "do everything in our power" to achieve their release.

He issued a similar appeal last week in a 34-second video made available in the internet, which ended with the ICRC president saying "please release them."

Philippines Interior Secretary Ronaldo Puno on Monday urged the Abu Sayyaf members to reconsider their "impossible demands" and not harm the hostages.

"We hope this beheading will not be undertaken," he added.

He said the kidnappers demanded the repositioning of government forces who already pulled back by as much as 15 kilometres from the rebel encampment in Indanan town.

"We are very disheartened by these new demands," Puno said. "It is physically impossible to remove everybody within 24 hours."

On the weekend, soldiers, policemen and militiamen pulled out from Indanan town in a bid to save the hostages, giving the rebels around 130 square kilometres to move around freely.

When the military cordon was up, the kidnappers were restricted to only about 30 square kilometres in the jungles of Indanan.

Puno said under the new demand, "no place (on Jolo) will be immune from any threat."

Abu Sayyaf rebels have in the past beheaded hostages, including an American tourist abducted in 2001, when authorities failed to meet their demands.

There have been some public criticism in Switzerland over the handling of the situation, with some, including the family of Notter who is Swiss, saying the government was not doing enough to ensure the release of the aid workers.

Swiss Foreign Minister Micheline Calmy-Rey, who met with Notter's family, said diplomats were working on the case.

The Red Cross workers were abducted on January 15 after visiting the provincial jail on Jolo to oversee a water and sanitation project.

Abu Sayyaf rebels have in the past beheaded hostages, including an American tourist abducted in 2001, when authorities failed to meet their demands.

The guerrillas have been blamed for some of the worst terrorist attacks in the Philippines, as well as other high-profile kidnappings of foreigners. (dpa)