* ICRC president urges authorities to consider rebel demands * Appeal follows threat by abductors to behead hostage

GENEVA, March 27 (Reuters) - The International Committee of the Red Cross (ICRC) asked Philippine authorities on Friday to consider demands by Islamic militants holding three ICRC staff hostage to pull back their security forces.

The aid agency's president Jakob Kellenberger made the rare public appeal in response to the abductors' threats to kill one of the three aid workers on Monday if their demands were unmet.

Earlier in the day the Philippines rejected the demand from the al Qaeda-linked Abu Sayyaf rebels.

Interior Minister Ronaldo Puno described it as "impossible" and "unreasonable", but said the government may consider moving back a few kilometres away to allow negotiations to end the crisis. [nMAN503515]

The hostages -- Swiss national Andreas Notter, Italian Eugenio Vagni and Filipina Mary Jean Lacaba -- were seized on Jan. 15 after visiting a prison on the southern island of Jolo.

Kellenberger asked retired general Eduardo Ermita, the Philippine president's executive secretary, to ensure the country does everything possible to save the lives of the hostages, the ICRC said in a statement issued in Geneva.

"In particular, the ICRC president asked that the authorities consider the abductors' demand regarding the position of troops," it said.

The ICRC is often a discreet presence in the countries in which it operates, rarely speaking out in order to uphold its neutrality.

A military spokesman said in Manila this week that security forces are limiting food, water and other supplies to the rebels holding the ICRC staff in an attempt to force their release.

Although soldiers have stopped chasing the Abu Sayyaf rebels, they surrounded them in a remote region of Jolo and stepped up pressure on them, the spokesman said.

The Abu Sayyaf, a small Islamic militant group with ties to regional network Jemaah Islamiah, threatened to behead one of the hostages after a military firefight erupted nearly two weeks ago, killing nine people and wounding dozens.

The rebel group, notorious for kidnappings, has a history of beheading captives. Philippine newspapers have said that they demanded a ransom for the safe return of the ICRC staff, with one estimate put at $1 million.

"I am very concerned by the threats of the kidnappers," said Kellenberger, a former Swiss diplomat. "I am asking for their safe, unconditional and immediate release." (Reporting by Stephanie Nebehay; Editing by Katie Nguyen)

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