An audio tape said to have been recorded by al-Qaeda leader Osama Bin Laden has called on his supporters to attack Gulf oil supplies.
Bin Laden was last seen in a video shortly before the US election
The recording, posted on an Islamic website, has not been verified.
In the message a speaker identified as Bin Laden also praised the attack by a group of militants on a US consulate in Saudi Arabia on 6 December.
The voice blamed Saudi leaders for unrest in the kingdom, accusing them of "violating God's rules".
Earlier this month Pakistani President Pervez Musharraf said recent intelligence proved that the al-Qaeda leader was alive - but he said the trail was "completely cold".
'Mercy for mujahideen'
"Targeting America in Iraq in terms of economy and loss of life is a golden and unique opportunity... Be active and prevent them from reaching the oil, and mount your operations accordingly, particulary in Iraq and the Gulf," the speaker said.
The speaker also said: "We ask God Almighty to have mercy on the mujahideen who stormed the consulate of the Americans in Jeddah."
Saudi Arabia has been battling a wave of attacks in the past 18 months, which it blames on the al-Qaeda network.
Nine people, including four militants, were killed when militants stormed the US building in Jeddah on 6 December. A fifth militant was arrested at the scene of the attack, which was claimed by the group.
Saudi-born Bin Laden has repeatedly called for the toppling of the kingdom's ruling family.
"The responsibility for the current situation in Saudi Arabia rests with the regime," the recording said, according to AFP news agency.
"In Saudi Arabia, it is the king and not Allah who commands sovereignty and complete obedience."
The speaker said he had advised the government two decades ago to "remedy the situation", adding: "it has not changed at all".
In Washington, Secretary of State Colin Powell said US intelligence officials were analysing the tape, the Associated Press news agency reported.
"It appears to be" the voice of Bin Laden, Mr Powell said.
The last appearance of the militant leader was just before the US election on 2 November, in a video tape in which he threatened fresh attacks on the US, whoever was elected.
He appeared in good health in the tape, but it was not clear when it was recorded.
Bin Laden is widely believed to have been hiding in the mountains along the
Pakistan-Afghanistan border since US-backed forces toppled Afghanistan's Taleban regime in late 2001.