The first explosion at about 8:35 p.m. (12:35 p.m. EST) shattered windows and sent smoke and flames rising into the nighttime sky near the Saudi Interior Ministry in central Riyadh.
A police official said the second explosion, about an hour later, took place in a center for recruiting emergency troops located five miles from the scene of the first explosion. He said the cause of the two explosions was not immediately clear, but that a car bomb was suspected in the first blast. Al-Arabiya television reported the second explosion was part of a failed attempt to storm the recruiting center.
An Interior Ministry official said a number of police were injured in the first blast. There were no immediate reports of casualties in the second.
At about the same time, a police official said, Saudi security forces and suspected militants clashed in northern Riyadh, with the suspects firing guns and lobbing grenades.
The Saudi government has been cracking down on militants since a series of al Qaeda-affiliated attacks on residential compounds in May 2003. The attacks have killed several Westerners. Many senior militants have been either killed or arrested in the campaign, including more than half of a list of 26 most-wanted terrorists.
Early Wednesday, a suspected terrorist was killed in Riyadh after tossing a bomb and shooting at security agents, according to a security official who spoke on condition of anonymity. On Tuesday, another suspect and a bystander were killed in a shootout in the same Riyadh neighborhood, according to an unidentified Interior Ministry official said. One suspect was captured in that attack.
The sirens of ambulances and police cars were heard in the area of the blasts Wednesday night. Smoke rose from a traffic tunnel near the ministry, and three helicopters hovered. Police sealed off roads leading to the area.
The Interior Ministry, a massive, modern high-rise, was shown with its windows brightly lit in pictures broadcast from the scene by Saudi television. Ambulances raced into the complex. A Saudi TV correspondent said witnesses reported hearing shooting before the explosion.
The Saudi correspondent added windows of almost all the buildings close to the interior ministry were damaged and shrapnel fell far from the site.
An official in the ministry told The Associated Press the explosion rocked the ministry building and shattered some of its windows. Fire was seen in the area, the official said.
On Dec. 6 Saudi militants attacked the U.S. consulate in Jiddah, killing nine people.
Wednesday's blasts and the attack on the consulate constituted an upsurge in violence that was accompanied by a Dec. 16 message from Saudi-born al Qaeda chief Osama bin Laden. In the tape, bin Laden's first directed specifically at Saudis in years, he praised those who attacked the U.S. consulate and advised his followers to attack the kingdom's oil installations to weaken both the West and the Saudi royal family.
In May, Saudi militants attacked oil company compounds in Khobar, 250 miles northeast of Riyadh, and killed 22 people, 19 of them foreigners. Earlier the same month, attackers stormed the offices of an American company in Yanbu, 220 miles north of Jiddah, killing six Westerners and a Saudi. All four attackers died in a shootout after a police chase in which they dragged the body of an American from the bumper of their car.
On April 21, five people, including two senior police officers and an 11-year-old girl, were killed along with the suicide bomber in an attack on a government building in Riyadh.
In November 2003 a suicide bombing at a Riyadh housing compound killed 17 people, most of them Muslims working in Saudi Arabia.