Manila, Philippines ? Muslim extremists holding American missionaries hostage ruled out further negotiations 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.

Martin and Gracia Burnham

“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 for a six-month mission to train Filipino troops.

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.