The US Embassy in Saudi Arabia said Westerners face possible attack from unidentified extremists in the central province of al-Qassim, in the first warning of its kind this year.

"We have received credible information that an unidentified extremist(s) in Saudi Arabia may be planning to attack Westerners working and living in al-Qassim, Saudi Arabia," the embassy said in a statement posted on its website.

"The timing and method of potential attacks are currently unknown," said the statement dated August 4, urging US citizens to "exercise prudence and enhanced security awareness at all times".

Mansour al-Turki, spokesman for security affairs at the Interior Ministry, said he could not immediately comment.

Militants carried out attacks against Western targets, government symbols and oil facilities between 2003 and 2006. The attacks included suicide bombs at Western housing compounds, the interior ministry's headquarters in Riyadh and oil and petrochemical companies, plus an attempt to storm the world's biggest oil processing plant at Abqaiq in 2006.

A large-scale security crackdown and a rehabilitation programme of militants sponsored by pro-government clerics have helped Saudi security services to stay ahead of plots to destabilise the country's absolute monarchy in recent years.

But concerns over the security situation in the kingdom resurfaced after its top anti-terrorism official, Prince Mohammed bin Nayef, was slightly hurt in a suicide attack in his house in September by a Saudi posing as a repentant militant returning from Yemen.

Saudi Arabia arrested 113 mainly Saudi and Yemeni al Qaeda-linked militants in March, including two suicide bomb teams. – Reuters