SAUDI security forces today killed five men believed to be linked to a bid to blow up the world's largest oil-processing plant, a police officer at the site said. "Five armed wanted men were killed today," in the clashes in a residential Riyadh suburb, the police officer on the scene told AFP.He said large quantities of arms and explosives as well as material destined to prepare car bombs have been seized in the house where the suspects were holed up. He said the suspects used grenades in their bid to flee authorities.