This picture taken from an Islamic website shows Paul Johnson after he was abducted by al Qaida militants on June 15. (AFP)

Dubai, June 18 (Reuters): Al Qaida militants beheaded an American engineer they had held hostage since last week after the Saudi government failed to meet its demands to release jailed militants, an Islamist website said today.

“As we promised the mujahideen, we have beheaded the American hostage Paul Marshall Johnson after the deadline that the mujahideen gave to the tyrannical Saudi government passed,” a statement signed by the Organisation of al Qaida in the Arabian Peninsula said on the al Islah website.

The website showed three pictures of what appeared to be Paul Johnson’s severed head. One showed the bloodied head propped up on the back of a body in an orange uniform with a knife on the face.

A second picture showed a hand lifting up the head and a third image showed the body and the severed head from a different angle. “This act of revenge is to heal the hearts of believers in Palestine, Afghanistan, Iraq and the Arabian Peninsula,” the statement said.

“This is God’s voice rising in anger... at the treatment of Muslims in Abu Ghraib, al-Hair (prison), Guantanamo, Ruwais (Saudi prison) and others,” it added, referring to US military prisons in Abu Ghraib, Iraq and Guantanamo Bay, Cuba.

Johnson was an employee of defence contractor Lockheed Martin, which manufactures US helicopter gunships.

The statement said al Qaida had killed him because of “what Muslims have suffered from American Apache planes and their rockets”.

Earlier today, thousands of Saudi security officers backed by FBI agents scoured Riyadh for Paul Marshall, while the engineer’s family pleaded for his life before the deadline expired.

“Please release my father. He is an innocent man. He loves Muslims. Saudi Arabia was his home,” Johnson’s son Paul told Dubai-based Al Arabiya television from the US.

Johnson’s Thai wife Thanom urged US authorities to save her husband. “When I see pictures of my husband, I hurt so much, I fall to the floor,” she said in broken English. “He is sick man, he need medicine. He hasn’t done anything wrong.”

A senior Saudi official in Washington, who declined to be named, said a team of about 20 FBI agents specialised in hostage rescue and negotiations were working alongside the Saudis.

He said that for the past two days, more than 15,000 Saudi officers and security forces have been searching throughout Riyadh for Johnson, going door-to-door in some neighbourhoods considered hotbeds for al Qaida militants and sympathisers.