Saudi forces have killed five suspected insurgents believed to be linked to an al-Qaida attack on a major oil facility, security sources said.

A firefight ensued at dawn on Monday after security forces besieged the men, who were hiding in a villa in the affluent al-Hamra district of east Riyadh where several Western residential compounds are.

Witnesses said they heard the sound of heavy gunfire and what appeared to be mortars as security forces surrounded the area and sealed it off before dawn.

The shoot-out ended after two hours with the death of all of the men inside the building, the security sources said.

One source said the men were traced partly through internet surveillance. An internet statement was issued at the weekend claiming that al-Qaida was behind an attack on the world's largest oil-processing plant in Abqaiq on Friday.

Authorities say two of the bombers were on a list issued last year of top wanted al-Qaida-linked Muslim fighters.

Suicide bombers attempted to penetrate the world's largest oil-processing plant at Abqaiq, in the oil-rich eastern province on Friday, but their attack was thwarted, leaving two security men dead.

At least four attackers and two security guards were reportedly killed in the attack.

Al-Qaida claim

Abqaiq handles crude pumped from the giant Ghawar field and ships it off to terminals Ras Tanura, the world's biggest offshore oil loading facility, and Juayma.

It also pumps oil westwards across the kingdom to Red Sea export terminals.

An al-Qaida statement posted on the internet claimed responsibility for the attack by two "martyrdom-seekers" in what the group said was a successful attack, vowing defiantly to attack more Saudi oil installations.

The posting attributed to the group named the attackers as Muhammad al-Ghaith and Abd Allah al-Twaijri - both on a list of top wanted Saudi insurgents - and said Friday's attack was in response to a call by al-Qaida leader Osama bin Laden to target oil installations.

"We shall not cease our attacks until our territories are liberated," said the statement, adding that the operation was successful and that some attackers got away.

Vow to crush

The statement said the attackers were able to get through two gates and blew themselves and their vehicles up as planned, rejecting Saudi state media reports that security forces stopped the attackers.

"We renew our vow to crush the forces of the Crusaders and the tyrants and to stop the theft of the wealth of the Muslims," said the statement signed by al-Qaida in the Arabian Peninsula.

The authenticity of the statement, posted on a website often used by Islamist groups in Iraq, could not be verified.

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