Al-Qaeda militants said tonight they beheaded a US engineer they had held hostage in Saudi Arabia since last week and displayed his severed head in pictures posted on an Islamist website.
Al-Qaeda had said the Saudi government had until today to free jailed militants or it would kill Paul Marshall Johnson.
"As we promised the mujahideen, we have beheaded the American hostage Paul Marshall after the deadline that the mujahideen gave to the tyrannical Saudi government passed," a statement signed by the Organisation of al-Qaeda in the Arabian Peninsula said on al Islah website.
The website showed pictures of what appeared to be Mr Johnson's severed head resting on his body.
The body was later found in a suburb of the Saudi capital Riyadh. The US Embassy confirmed Mr Johnson had been killed. "The inhumanity of the crime exceeds all boundaries of civilised peoples," US Ambassador James Oberwetter said in a statement.
Saudi forces later killed three wanted militant suspects in Riyadh.
Mr Johnson, an employee of US defence contractor Lockheed Martin, 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 Mr Johnson.
Saudi officials had said the kingdom would not give in to the group's demands.
Mr Johnson's kidnapping, which follows a spate of suicide bombings and shootings in the past six weeks, has raised the stakes in al-Qaeda's war against the Saudi government.