According to Dr Said bin al-Ziar's son, his father was arrested in the early hours of Saturday morning.

"Saudi security authorities have so far issued no official charges against my father," said Abd Allah al-Ziar.

"Apparently, he had been arrested after participating in Aljazeera's special coverage on Usama bin Ladin's audiotape aired on the television channel last Thursday," he told Aljazeera.

Dr Al-Ziar's son said "we cannot contact my father now." He said the authorities who carried out the arrest said Dr al-Ziar would be taken to the "Hayl prison".

"I feel disappointed as he was taken to jail again without any charges levelled against him."

Dr al-Ziar was previously jailed for eight and a half years on charges of calling for reform in the Saudi kingdom. He was released 14 months ago.

Car bomb defused

Meanwhile, Saudi police have defused a car bomb in the kingdom, Saudi state television said on Saturday.

The explosive-rigged vehicle is the third police have defused since Tuesday, when two similar car bombs were found north of the capital Riyadh.

State television did not say where the vehicle was found and an Interior Ministry official declined to give details about the incident.

Last week unidentified gunmen killed five policemen in fierce clashes in and around Riyadh.