RIYADH, June 16: Captors of American hostage Paul M. Johnson have threatened to kill him by Friday if their supporters held in the kingdom's prisons are not released before the expiry of their '72 hours deadline'.

"If the Saudi government wants Paul Marshall Johnson to be released, it must free the mujahideen held in the prisons of Hair, Al Ruwais and Allecha within 72 hours... Otherwise, we will execute him to avenge our Muslim brothers'," a video statement signed by "Al Qaeda in the Arabian Peninsula" said.

The statement, whose authenticity could not be confirmed, carried images of the blindfolded hostage. Johnson gave his identity and nationality, saying that he was working as an aviation engineer.

"My name is Paul Marshal Johnson, and I am a citizen of the United States," says a slurred voice with American accent in the recording on a website. "I work for Apache helicopters."

Then an armed man wearing balaclava and a belt of explosives introduces himself as Abdel Aziz Al-Muqrin, leader of an "Al Qaeda in the Arabian peninsula" group.

He reads out a lengthy statement warning that "rivers of the blood of other Crusaders would be spilled this year in the Arabian peninsula". Meanwhile, Adel Al-Jubeir, foreign policy adviser to the Saudi crown prince, reiterated that Riyadh would not negotiate with the 'terrorists' threatening to execute the American hostage.