Riyadh  (AsiaNews/Agencies) - American hostage Paul Johnson has been beheaded in Saudi Arabia and his severed head displayed in pictures on an Islamist website.  "We have beheaded the American hostage Paul Marshall [Johnson] after the deadline that the mujahedeen gave to the tyrannical Saudi government passed," a statement signed by the Organisation of al-Qaeda in the Arabian Peninsula said on the al-Islah website.

"The infidel got his fair treatment. Let him taste something of what Muslims tasted who were long reached by Apache helicopter fire and missiles."

The website showed three pictures of what appeared to be 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.

Soon after the pictures appeared the website was inaccessible.

Johnson, an engineer who worked on Apache helicopters for US defence contractor Lockheed Martin, was kidnapped last weekend by terrorists who threatened to kill him if the kingdom did not release its al-Qaeda prisoners.

He was the first westerner to be kidnapped in a wave of militant attacks in the kingdom that began more than a year ago.

Al-Qaeda said it carried out the attacks and kidnapping to avenge US abuse of Muslim prisoners. On Tuesday, the group released a video on a website showing a blindfolded Johnson.

Shortly after the announcement, Saudi security sources said they had killed three militants in a gun battle in the capital, Riyadh. A senior security source said Abd al-Aziz al-Muqrin, 31, was among those killed. It was reported he was surrounded after dumping the body of the American.

Al-Arabiya television named the two other militants as brothers Faisal and Bandar al-Dakheel, who were on a Saudi interior ministry list of 26 top fugitives in the kingdom.

Saudi security forces had surrounded the militants in the Malazz district of Riyadh after the body of the kidnapped American, Paul Johnson, 49, was found earlier in the evening.

The kidnapping of Mr Johnson sparked unprecedented public appeals from moderate Saudi clerics and lawyers, saying that he was an invited guest to the country, protected by Islamic law.

One Saudi colleague of Mr Johnson, using the pseudonym "Saad the believer", said he had often invited the American to his home for dinner, and given him books about Islam as presents, and invoked the traditional tribal protection over him, known as ijara.

If Johnson is harmed, the Saudi wrote: "I will never forgive you, I will curse you in all my prayers."

The kidnapping triggered a fierce debate on prominent Islamic websites. One senior Saudi cleric, Sheikh Abu Bassir, re-issued a religious ruling stating that foreigners arriving in Saudi Arabia on valid visas should be protected.