A Saudi opposition group said as many as 144 inmates and 40 security men died in a fire Monday at Saudi Arabia's largest prison, more than double the official toll given by authorities.

"According to an unimpeachable security source, 144 inmates have died in the fire at Al-Hair prison, in addition to 32 policemen and eight police officers," London-based Saad al-Fagih of the Movement for Islamic Reform, which was first to break news of the blaze, told AFP.

Saudi Arabia's prison chief, quoted by the official SPA news agency, said earlier that the Riyadh jail blaze "left 67 inmates dead, as well as 20 inmates and three security men wounded."

AFP from Riyadh adds: Investig-ators yesterday ruled out sabotage as a cause of a blaze at the Saudi prison, where the war against Islamist extremists linked to Al-Qaeda is raging.

The authorities were working on the theory that an accident caused what Al-Watan newspaper described as the "worst catastrophe ever" at a Saudi pentitentiary.

A committee was set up immediately by Interior Minister Prince Nayef bin Abdul Aziz to investigate the cause of the fire, but a high-level security source quoted by the Saudi-

owned daily al-Hayat ruled out "any act of sabotage".

Al-Hayat said the facility houses foreign as well as Saudi common law prisoners.

Prison service chief Major General Ali Hussein al-Harethi told the news agency that a sponge mattress caught fire in a cell housing 20 inmates in wing 19 of the jail, setting off the blaze.

The stricken wing accommodates around 200 inmates.

Three helicopters backed by dozens of ambulances evacuated the casualties.

A massive security cordon was thrown around the prison and al-Ryad newspaper reported that it provoked a traffic jam so bad that there were numerous crashes.

Movement for Islamic Reform said security forces, apparently fearing an attack, stopped and searched civil defense cars and ambulances, delaying rescue efforts and causing the toll to rise.

The security cordon also prevented people from fleeing, leaving many to suffocate to death, charged Saad al-Fagih of the Saudi opposition group.

He insisted the fire broke out in the morning, several hours before authorities announced it, and charged that the high toll was partly caused by the authorities' handling of the tragedy.