Al Qaeda guerrillas have showed images of a blindfolded American hostage and said they would kill him if the Saudi government failed to free jailed militants within 72 hours.
The threat to kill Paul Marshal Johnson follows a spate of suicide bombings and shootings in the past six weeks. The kidnapping has raised the stakes in al Qaeda's war to topple the kingdom's pro-US monarchy and drive out Westerners from the world's largest oil exporter.
"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. They have 72 hours from today or else we will sacrifice him," said an al Qaeda statement carried on Sawt al Jihad Web site.
On Saturday, al Qaeda said it was holding Johnson, a US engineer and the first Westerner to be kidnapped in a wave of militant attacks in the kingdom that began more than a year ago. It also claimed responsibility for killing American Kenneth Scroggs, who was shot dead as he parked his car in his villa.
Concerns about security in Saudi Arabia had helped push world oil prices to record highs recently before oil producers said they would increase output.
The leader of al Qaeda in Saudi Arabia, Abdul Aziz al-Muqrin, promised in earlier statements that 2004 would be "bloody and miserable" for the kingdom.