Saudi security forces shot dead five suspected terrorists and arrested a sixth early today in raids in Riyadh in pursuit of those responsible for the weekend attack on the huge oil processing complex in eastern Saudi Arabia, the Interior Ministry said.

"We think all the men involved had something to do with Abqaiq attempt," Lieutenant General Mansour al-Turki, the chief spokesman for the ministry, said referring to Friday’s attempt by suicide bombers to detonate car bombs inside the world’s biggest oil stabilization plant.

Security forces raided two houses in eastern Riyadh, one in the Yarmouk district, that had been under surveillance, General al-Turki said. Five suspects were shot dead in the Yarmouk house, and a sixth man was detained in the second house. The security forces were said to suffer no casualties.

"After an intense shootout, the security forces managed to kill all the five terrorists in a short time," the Interior Ministry said in a statement, which described the Yarmouk house as a "den of aggression".

Earlier today, the Saudi-owned Al-Arabiya television quoted Saudi security sources as saying the forces exchanged fire with the suspected terrorists for about two hours. Police said they confiscated weapons and ammunition from the house in the suburb where the suspects had been hiding, the Dubai-based channel reported.

Friday’s attack, the first ever on Saudi Arabia’s vital oil infrastructure, was claimed by the Saudi branch of al-Qaeda in an internet posting. Two suicide bombers were killed in the attack, which was foiled when security guards fired at their vehicles outside the gates to Abqaiq, which processes about two-thirds of the country’s oil before it is exported. The guards died of their wounds.

The Interior Ministry identified Friday's assailants as Abdullah Abdul-Aziz al-Tweijri and Mohammed Saleh al-Gheith and said both were on a list of the 15 most-wanted terrorists the kingdom issued in June. The deaths of the two meant that only four remain at large of the list of 15. Ten have now died or been killed, and one was previously arrested.

Witnesses to Friday’s attack reported that security forces traded fire with gunmen outside the processing plant after the explosions and that a hunt for attackers continued for hours. Saudi officials have not reported the capture of any assailants.

The Saudi branch of al-Qeida warned in its internet statement on Saturday that its suicide bombers would strike the oil industry again.

Al-Qaeda militants launched a campaign of violence in Saudi Arabia in 2003. The country is the birthplace of Osama bin Laden. Saudi security forces have largely had al-Qaeda militants on the run for the past year, arresting hundreds of suspects. They killed or captured all but one of the top 26 militants on a most-wanted list issued in December 2003, then issued the second list in June.

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