The US government has strongly urged all its citizens to leave Saudi Arabia after an al-Qaeda group there beheaded the kidnapped US hostage, Paul Johnson, writes Conor O'Clery in New York.
Gruesome pictures of the severed head of Mr Johnson were shown on a number of US media websites yesterday, fuelling a sense of outrage across the country.
The Secretary of State, Mr Colin Powell, said the US "totally condemned this act of barbarism" and that America and its Saudi Arabia allies would "redouble our efforts to go after terrorists wherever they are".
"America will not be intimidated," President Bush said, condemning the murder as cold- blooded.
The US ambassador in Riyadh, Mr James Oberwetter, said: "The inhumanity of the crime exceeds all boundaries of civilised peoples."
Last night, the man believed to lead al-Qaeda in Saudi Arabia, Abdulaziz al-Muqrin, was reported to have been killed by Saudi security forces. He is believed to have died with two associates in a shoot-out.
Mr Johnson was kidnapped last weekend and is the third US citizen to be murdered in Saudi Arabia in the last 10 days. News of his beheading was posted on an Arabic website along with several photographs showing the head placed on the back of a body wearing an orange jumpsuit, with the face turned towards the camera. Shortly afterwards his body was reported found in the Saudi capital, Riyadh.
Mr Johnson, who had lived 12 years in Saudi Arabia, worked on targeting and night vision systems for Apache helicopter systems for Lockheed Martin. The day he was seized, Islamic militants shot dead another American - Kenneth Scroggs, from New Hampshire. On June 6th, Irish journalist Simon Cumbers (36) was shot dead in Riyadh and BBC correspondent Frank Gardner seriously injured.
The militants holding Mr Johnson demanded the Saudi authorities release by yesterday other militants detained in recent weeks and months in response to growing terrorism. The government refused.
In New Jersey, where Mr Johnson's family lived, a US flag and yellow ribbons hung from the front porch of his sister, Ms Donna Mayeux. Hundreds of supporters held candlelight prayer vigils on Thursday night.