WASHINGTON - The US Embassy in Saudi Arabia warned on Wednesday that a terrorist group may be planning to abduct Westerners in the capital, Riyadh, and urged US citizens to exercise caution.

"US Embassy in Riyadh advises US citizens in the Kingdom of Saudi Arabia that we have received information that a terrorist group in Saudi Arabia may be planning to abduct Westerners in Riyadh," the embassy said in a message posted on its website.

"The US Embassy in Riyadh reminds all US citizens to exercise prudence and enhanced security awareness at all times," the message said.

The message gave no further details on the information received by the embassy, and advised US citizens to carry out regular security measures including varying personal travel routines and minimizing their public profile.

A US diplomatic source told Reuters in Dubai that the warning was based on "solid information" but that the embassy had no plans to reduce the hours it was open or repatriate any staff or their family members.

A Saudi interior ministry official, contacted by Reuters, said he had no information about the threat that prompted the US warning.

In Washington, State Department spokeswoman Heidi Fulton said underscored that the embassy statement was issued "specific to a new threat to abduct Westerners in Riyadh" but declined to provide further details.

"We do not comment on specific intelligence, as doing so threatens to undermine intelligence operations that are critical in protecting the United States and our allies," she said in an emailed statement.

Al Qaeda launched a campaign of attacks in Saudi Arabia in 2003 which fizzled out in 2006 but the government fears al Qaeda militants could use their base in Yemen to restart operations.

The government also fears that Shi'ite Iran could stir up dissent among minority Shi'ites to destabilize the kingdom, home to Islam's holiest sites.

Saudi Arabia, a key US ally and the world's leading oil exporter, has no political parties and its parliament is an appointed body with limited powers.

The former head of Saudi Arabia's intelligence agency said on Monday the kingdom was sure its 35,000-strong security force can protect oil installations from what he said was the rising threat of attack in the region.

Prince Turki al-Faisal told an audience in Madrid that the wave of of unrest rippling across the Arab world has created fertile ground for terrorist groups but that the kingdom itself remained "stable and secure."