A radical Islamist militant group has claimed responsibility for a suicide bomb attack in the Saudi capital, Riyadh, that killed four people.
The blast wrecked the security forces headquarters in Riyadh
The al-Haramain Brigades, a group linked to the al-Qaeda network, said it had bombed the security forces' HQ.
The car bomb attack on Wednesday killed four people, including two security officials, and injured at least 148.
The group's claim has not been verified independently, but Saudi officials had already blamed al-Qaeda for the attack.
"Who else sends suicide bombers to blow up cars in the midst of urban centres?" an official told reporters.
The claim of responsibility came in a statement published on at least two Islamist websites.
The group said it followed the path of Osama Bin Laden and al-Qaeda against the Saudi authorities.
The group said it was responsible for an attack in Riyadh in December 2003 against a Saudi security services official. A bomb exploded in the official's car, but caused no casualties.
In the Saudi Arabian context, the name of the group is highly provocative. The world Haramain refers to the Islam's holiest mosques in Mecca and Madina.
The Saudi king, Fahd, asserted his political and religious legitimacy by taking on the title of Custodian of the Two Holy Mosques in 1986.
Al-Qaeda supporters have been blamed for blasts in Riyadh last year, as well as the 11 September 2001 attacks in the US and explosions in Madrid and Bali.
US President George W Bush said those responsible wanted to destabilise Saudi Arabia.
"The attack again today on Riyadh was a reminder that there are people that would like... to overthrow the ruling government," he told a meeting of US newspaper editors.
"They certainly want to frighten everybody and kill as many as they can," he added.
The US ordered its non-essential staff to leave Riyadh last week.
Wednesday's attack happened at 1400 (1100 GMT) near the General Security building on al-Washm Street in Riyadh's central Nasiriya district.
Television pictures showed that the explosion had caused widespread damage to the facade of the building and destroyed a number of cars.
Police have repeatedly clashed with Islamic militants around Riyadh in the last fortnight and officials say they have intercepted five vehicles packed with explosives.
Crown Prince Abdullah, the effective ruler of Saudi Arabia, said last Monday that terrorism would be confronted and every citizen was now a member of the security forces.
BBC Middle East correspondent Paul Wood says the Saudi royals seem now to have realised they are in a fight for their very survival as rulers of the state which carries their name.
Riyadh suffered two major suicide bombings in 2003.
A total of 51 people were killed in the attacks in May and November, including the bombers themselves.