Facades were torn off buildings near the explosions, revealing rooms still ablaze. Cars were smashed by debris. Clouds of dust and black smoke rose from the building and settled over the neighborhood.
A Saudi Interior Ministry statement said attackers tried to drive one vehicle into the building, which housed the headquarters of Riyadh's traffic department in addition to the General Security headquarters.
The driver exploded the car 100 feet away from the gate, the Interior Ministry official said.
While the statement referred to just one car bomb, a police official had told The Associated Press earlier that two cars with bombs were parked about 50 feet away from the building. He added "a number of charred bodies" were carried from the scene.
The police official had said the blasts appeared to have resulted from suicide attacks and that one assailant died and one police officer was also killed.
Staff at three hospitals said nine people were killed, including policemen and civilians, and 125 were wounded. The hospital officials spoke on customary condition of anonymity.
A Saudi official told the AP that Deputy Secretary of State Richard Armitage met with Saudi Foreign Minister Saud al-Faisal about 30 minutes after the attack. The meeting was at the Foreign Ministry, which is close to the General Security building in al-Nassiriyah, a central Riyadh neighborhood.
Rescue workers searched through rubble to recover bodies and survivors.
The General Security building, the administrative headquarters of the Saudi domestic security service, was severely damaged in the bombing that came just days after the United States warned of possible terror attacks in the kingdom.
General Security oversees officers who investigate burglaries and murders, direct traffic and perform other basic police duties. Such officers have been on the front lines in a Saudi crackdown on Islamic militants, manning checkpoints as part of stepped up security and occasionally engaging in fire fights with suspects.
Last month, a purported al Qaeda message appeared on the Internet threatening Saudi police, members of the intelligence forces and other security agents. The message said targeting Saudi security agents "in their homes or workplace is a very easy matter."
The Foreign Ministry is located behind the General Security building in al-Nassiriyah, a central Riyadh neighborhood.
The explosions, which occurred about 2 p.m. local time (7 a.m. ET), hit when workers would have been leaving for the Saudi weekend.
Saudi television showed the General Security building, about seven floors, with its glass facade shattered and severe damage inside. Firefighters worked to extinguish the blazes, and more than 20 ambulances had arrived. Two helicopters flew above the site. Police blocked the area and evacuated the surrounding buildings.
Hanan Batteesha, an Egyptian woman, was with her two children, aged 11 and 14, when she heard a "big blast."
"We heard wails and cries, then saw our neighbors running down the stairs," she said.
By the time they reached the ground floor, "the gate was damaged, windows started shattering, and glass fell all over us," she said. "The fronts of the buildings around us were damaged, the air conditioners mangled and there was smoke everywhere."
The blast was heard and felt more than three miles away.
In an interview with the Saudi TV station Al-Ekhbaria, a leading Saudi cleric called the bombing "a dastardly criminal act."
"How can they make these dastardly acts bring them closer to God?" Sheik Abdullah Al-Mutlaq said, apparently alluding to Islamic militants who are blamed for terrorist attacks in the kingdom.
The explosions came only days after Saudi authorities announced they had seized three booby-trapped SUVs that were loaded with a total of more than four tons of explosives and had apparently been abandoned by militants involved in a shootout with security forces.
An April 12 shootout in Riyadh left one suspected militant and one policeman dead. The next day, militants opened fire at a checkpoint in Riyadh, killing four police officers. Eight people have been arrested in connection with the shootouts.
The United States last week ordered the departure of nonessential U.S. government employees and family members from Saudi Arabia. It also urged private citizens to leave the kingdom, and the U.S. Embassy in Riyadh issued an advisory, warning of "credible indications of terrorist threats aimed at American and Western interests in Saudi Arabia."
"Credible information indicates that terrorists continue to target residential compounds in Saudi Arabia, particularly in the Riyadh area, but also compounds throughout the country," the warning read.
It was only the latest in a string of alerts issued by Western governments to citizens living or visiting in Saudi Arabia. In December and again in March, security at U.S. diplomatic offices was upgraded.
Last year, the Saudi capital suffered two major attacks by suicide bombers driving vehicles filled with explosives. A total of 51 people were killed in the May and November bombings, including the assailants.
The Saudis pursued terrorists and Islamic extremists vigorously after those attacks, arresting hundreds of people.
The attacks were blamed on Osama bin Laden's al Qaeda, the network accused of masterminding the Sept. 11, 2001, strikes in the United States.
There are some 200 to 300 nonessential U.S. officials and family members in Saudi Arabia, and some 30,000 U.S. citizens in all.