Updated

Muslim extremists holding American missionaries hostage ruled out further negotiations on Wednesday and threatened to kill the Kansas couple if U.S.-backed pursuit of the outlaws gets too close.

The Philippine military vowed, meanwhile, to intensify its drive to wipe out the Abu Sayyaf extremists and rescue Martin and Gracia Burnham of Wichita, Kan.

"If we see that the fight is getting one-sided, maybe we will just say goodbye to these two," Abu Sayyaf leader Abu Sabaya told Radio Mindanao Network in a what appeared to be a satellite telephone call Wednesday.

Sabaya made a similar statement shortly before he beheaded another kidnapped American, Guillermo Sobero, last July in what he called a birthday present to President Gloria Macapagal Arroyo.

"We prefer to prolong the hostage crisis and to give more embarrassment to the superpower (the United States) and the AFP (Armed Forces of the Philippines)," Sabaya said. "They cannot do anything to us.

The United States has sent about 1,000 soldiers, including 160 from the Special Forces, for a six-month mission to train Filipino troops to better fight the Abu Sayyaf.

The Burnhams and Filipino nurse Ediborah Yap are the last hostages from an Abu Sayyaf kidnapping spree that started last May 27.

The conflicting threats Wednesday came after a week of renewed activity in the 11-month-old saga that has hurt the Philippines' image, emboldened other kidnap gangs and become an extension of the U.S. war on terrorism.

Last month, Burnham's father went on local radio to accuse the Abu Sayyaf of reneging on an agreement to release the pair. Sabaya responded by offering "last deal" talks. The Philippine government then stepped in to say it would only accept the unconditional surrender of the militants and release of the hostages.

Sabaya's Wednesday response was chilling.

"We are accepting the challenge of the Philippine government. ... The door is closed for negotiations. It's up to them if they want to look for the dead bodies."

There have been only fleeting glimpses of the hostages over the months and indications they may be chained to their captors as human shields while they are dragged through Basilan island's thick jungle.

Sabaya's usual taunting style was certain to hit a nerve for the Philippine president, who has vowed several times to "crush" the Abu Sayyaf only to see pursuit of them drag on. She has suffered through criticism and protests over her decision to bring in U.S. troops, a move that was an extremely sensitive in the former American colony that canceled leases for U.S. military bases here a decade ago.

The military's reputation has been hit hard, with the pursuit underscoring all of its shortcomings. The Abu Sayyaf snatched a group of 21 people from a tourist resort and escaped in speedboats that outran the Philippine navy's vessels. Days later, the army surrounded a hospital that the rebels raided, only to let them slip away. There were subsequent allegations of payoffs.

Paul Burnham, Martin's father, has refused to comment on reports some ransom already had been paid and that the Abu Sayyaf had then raised its demand.

"We are just hoping that something will work out so that they can get out as soon as possible," he said

Sabaya earlier denied U.S. reports that his group already has received $300,000 in exchange for the hostages.