The statement, along with three still photos, was posted on a Web site where the group frequently makes announcements. It appeared around that the time that a 72-hour deadline set by the kidnappers ended.

"In answer to what we promised ... to kill the hostage Paul Marshall after the period is over ... the infidel got his fair treatment," the statement said.

"Let him taste something from what Muslims tasted who were long reached by Apache helicopter fire and missiles," the statement said.

Johnson, who worked on Apache helicopter systems for Lockheed Martin, was kidnapped last weekend by militants who threatened to kill him by yesterday if the kingdom did not release its al-Qaeda prisoners. Saudi security forces launched an all-out search, going door-to-door in some Riyadh neighbourhoods, as Johnson's wife went on Al-Arabiya yesterday pleading for his release.

American Nicholas Berg, a businessman, was beheaded last month by his captors in Iraq and his last moments later appeared on a videotape posted on an al-Qaeda-linked Web site. US officials say al-Qaeda-linked Muslim militant Abu Musab al-Zarqawi may have been Berg's killer.