An Interior Ministry statement confirmed the blasts and said an investigation is under way.

A US State Department official said the United States believes three car bombs were detonated in front of three compounds housing US and other Western nationals.

No US officials are believed to live at the housing compounds, a State Department official said.

The Al-Hamra compound is located in eastern Riyadh on the road to the airport.

The other two locations were named as the Cordoval and Gedawal compounds by informed sources.

There was a fourth explosion at the headquarters of the Saudi Maintenance Company, also known as Siyanco.

The explosions occurred hours before US Secretary of State Colin Powell was due to arrive in the capital. It was not immediately clear if the incidents would affect his travel plans.

A resident of the Al-Hamra compound, where the blast took place, talked to Arab News moments after the explosion took place.

Nick, a European national, told Arab News that the incident took place at around 11.15 p.m. He said that he and his family were sleeping when they woke up to the sound of gunfire. Moments later, a loud explosion within the compound was heard followed by another bigger explosion.

A foreigner driving down Dammam Road on his way to Riyadh told Arab News that he saw a huge ball of fire and a thick black cloud of smoke rise above the capital.

The explosion was so powerful that it blasted windows and even doors off the villas of the residential compounds.

“I have a five-month-old baby. She was sleeping next to the window when the blast took place,” said Nick.

The European national, who works for a reputable international company, said that he was on the second floor of his villa when the gunfire and blasts were heard. His four daughters immediately took to the floor when the gunfire was heard, as they had been trained to do so.

Sirens from police cars and the sound of helicopters could also be heard hovering around the compound, he said.

Another resident said that he saw “scores” of bodies on the ground following the explosion at Al-Hamra compound.

“I do not want to cause panic. The security and police said they will handle the situation,” he said.

Al-Hamra compound houses many international residents living in the capital. Alongside with Arizona compound, and Granada Village, the three are the most elite compounds in Riyadh that are especially attractive to foreigners.

Last week, police had seized a huge stash of explosives, weapons and cash following a shootout with suspected terrorists in the capital. Interior Ministry said police were hunting “19 terrorists, 17 of them Saudis” who “intended to carry out acts of terrorism.”

Al-Majallah, a sister publication of Arab News, citing an e-mail message from a newly-appointed Al-Qaeda spokesman, Thabet ibn Qais, said last week that “an attack against America was inevitable.”

Al-Qaeda has “carried out changes in its leadership and sidelined the Sept. 11, 2001 team,” the magazine quoted Thabet as saying. “Future missions have been entrusted to the new team, which is well protected against the US intelligence services,” the magazine quoted Thabet as saying. “The old leadership does not know the names of any of its members.”

Militants have earlier launched two major attacks on US targets in the Kingdom since the 1991 Gulf War.

In November 1995, five Americans and two Indians were killed and 60 people injured in an explosion in a car park near a US-run military training center in Riyadh.

In June 1996, a bomb in a fuel truck killed 19 American soldiers and wounded nearly 400 people at a US military housing complex in Alkhobar.

A US troop withdrawal from Saudi Arabia has been one of the main demands of Al-Qaeda. The United States said on April 29 it was ending military operations in the Kingdom and removing virtually all of its forces after the Iraq war.

Earlier this month, the State Department warned US citizens against non-essential travel to Saudi Arabia, citing intelligence that terrorist groups may be in the “final phases” of planning attacks against the US community there.

“Information indicates that terrorist groups may be in the final phases of planning attacks against US interests in Saudi Arabia,” it said in a statement.

The State Department said it had no information about what the possible target or targets might be.