President Gloria Macapagal-Arroyo refused to negotiate with two Malaysian nationals chosen by the separatist Abu Sayyaf as emissaries, even as the rebels threatened to behead U.S. captives "within 72 hours" if the Philippines rejected their demand.

The government refused to replace William Castillo as its intermediary, presidential spo-kesman Rigoberto Tiglao said.

"We appeal to the Abu Sayyaf to open its lines of communication with Castillo," Tiglao said.
Tiglao also appealed to the rebels not to take the lives of innocent civilians. "This is against all tenets of Islam and humanity," he said, in reference to a threat by Abu Sayyaf spokesman Abu Sabaya that one of the three American hostages will be beheaded if the government refuses the group's request.

Sabaya speaking in Spanish and Tagalog had called Radio Mindanao Network, a station that has kept its lines open to the bandits to say "if they cannot respond to our demand, we will start 'cutting the ribbon' on the white captives," an expression meaning the three U.S. captives would be killed.

Christian missionary Martin Burnham, 41, his wife Gracia, 42, and California-based Guillermo Sobrero were among 20 tourists and hotel staff abducted from a Palawan resort on May 27. They are now with other hostages held by the group in Basilan.

Sabaya said they wanted to negotiate with the former lawmaker Dato Sairin Karno and wealthy Malaysian trader, Yusuf Handam. Both Karno and Handam were instrumental in the release of nine Malaysians kidnapped with 11 foreign tourists from a resort in Malaysia last April.

Malaysia too rejected the Abu Sayyaf's demands. Malaysian Ambassador to the Philippines, M.H. Arshad, said: "The Malaysian government did not authorise any private negotiators to open up talks with the Abu Sayyaf for the release of the Palawan hostages because this is an internal affair of the Philippine government."