The State Department in Washington has sounded an alert of possible al-Qaida attacks against Westerners and oil workers beyond Saudi Arabia to the entire Gulf region.
The notice came shortly after abducted American engineer Paul Johnson was beheaded in the kingdom.
A senior Saudi official, however, has criticised the US for issuing such warnings, saying they could help "militants" to spread fear in the oil-rich region that depends heavily on foreign workers.
President George Bush, who is campaigning for re-election as a strong leader in Washington's war on terrorism, has vowed not to yield ground to anti-Americanism. But his administration on Thursday strongly urged US citizens to leave Saudi Arabia.
"The US government has received information that extremists may be planning to carry out attacks against Westerners and oil workers in the Persian Gulf region, beyond Saudi Arabia," the State Department said in its Friday announcement.
The regional warning reflected the same range of potential dangers, such as capture of civilians and human bombings, as it had specifically for Saudi Arabia, but it did not advise Americans to leave the area as a whole.
Adil al-Jubair, a foreign-policy adviser to Saudi Crown Prince Abd Allah bin Abd al-Aziz, said he did not support such warnings.
"We believe that one of the objectives of the terrorists is to drive people out of Saudi Arabia and so as a consequence we believe that calls for withdrawing people from Saudi Arabia could inadvertently play into the hands of the terrorists," he told reporters in Washington.
A State Department official, who asked not to be named, said it would be irresponsible not to warn US citizens about the dangers in the region.
"Of course the Saudis don't agree with us telling people to leave. But you can't tell them (Americans) to hunker down and ride it out because the fact is they cannot be protected," he said. "That does not mean the United States of America, the US government, is not committed to working with Saudi Arabia."
The US has withdrawn all but essential staff from its embassy in Riyadh because of a perceived lack of security.
On Friday, al-Qaida abductors beheaded US national Paul Johnson and their leader was then killed in a shootout with security forces as he tried to dispose of the body, Saudi officials said.
Saudi Arabia has been battling an intensifying al-Qaida campaign to destabilise the government that has particularly targeted foreigners in the world's largest oil exporter over the last few months.