A government official in the Philippines says kidnappers holding three Red Cross workers have threatened to behead one of their captives Tuesday by 2 p.m. local time (0600 UTC) unless police and troops withdraw from Jolo island.

Authorities say the militant group Abu Sayyaf contacted the government late Sunday to demand a complete evacuation of government forces from Jolo, in the southern Philippines, by Monday night. The island nation's interior secretary, Ronaldo Puno, says it is physically impossible to comply with the new demand.

The International Committee of the Red Cross is appealing for the release of its three workers - Eugenio Vani of Italy, Mary Jean Lacaba of the Philippines and Andreas Notters of Switzerland - who were kidnapped on January 15th.

Pope Benedict also added his voice to the plea for the hostages' safety.

A Vatican communiqué Monday says the pontiff is urging that "humanitarian sense and reason prevail over violence and intimidation."

In his message directed to the kidnappers, ICRC president Jakob Kellenberger said the hostages were only helping people in need, and that no ideology or religious law could justify killing them.

Last week, the Philippine government withdrew troops from a portion of Jolo Island, in response to a pledge that one of the hostages would be freed. The transfer never took place, however.

Abu Sayyaf is a Muslim extremist group that says it is fighting for an Islamic state in the southern Philippines. Since its inception in the 1990s, the group has been involved in numerous kidnappings, bombings and some of the bloodiest attacks in the region.