An Islamist website has posted a video of a US citizen abducted on Saturday in the Saudi capital, Riyadh, with a threat to kill him.
Officials said the video was probably authentic
A blindfolded man is shown giving his name as Paul Johnson - that of the missing US defence industry employee.
A website statement demands the release of certain named militants held in Saudi Arabia within 72 hours, otherwise the hostage will be killed.
The group said it killed another US citizen, Robert Jacob, last week.
The Saudi authorities have launched a search for Mr Johnson, 49, of New Jersey.
'Rivers of blood'
Officials said the video was probably authentic.
It shows a man in a black hood reading a statement and carrying an AK-47 rifle. A subtitle names him as Abdullah-Aziz
Mr Johnson's Lockheed Martin ID card is also shown in the video, which has been aired by US broadcaster CNN.
"My name is Paul Marshal Johnson and I am a citizen of the
United States," he says.
Signed by the "Al-Qaeda Organisation in the Arabian Peninsula", the militants' statement is carried by a website which has carried Islamist messages in the past.
"If the tyrants in the Saudi government want to secure the
release of the American hostage, they must release our
mujahideen held hostage in its jails," the statement said.
"They have 72 hours from
today or else we will sacrifice him."
It said that if its supporters were not freed "rivers of the blood of other crusaders would be
spilled this year in the Arabian peninsula".
al-Jubeir, the foreign affairs adviser to Crown Prince Abdullah, told CNN there will be no negotiation.
"We don't negotiate with terrorists, hostage
takers because then you open the door to more hostage taking and
more terrorism," he said.
He added that it was not Saudi policy to exchange prisoners.
The abduction is the first of an expatriate in fresh violence in Riyadh where three Westerners were killed inside a week.
BBC cameraman Simon Cumbers was killed and security correspondent Frank Gardner seriously injured in a drive-by shooting while working in the al-Suwaydi suburb of the capital on 6 June.
Two days later, Mr Jacob was shot dead in the al-Khalij area and unknown gunmen killed another American, Kenneth Scroggs, apparently as he parked his car in the al-Malaz suburb, on 12 June.
Saudi officials insist there is no security crisis but other nations have advised their citizens to leave the country.
The US embassy has reiterated a warning to Americans in Saudi Arabia to leave the country.
Attacks on foreigners have been blamed on radical Islamists seeking to oust Saudi Arabia's ruling al-Saud family and to drive out all Westerners, correspondents say.