The bombers were reported to have detonated vehicles packed with explosives in the Al-Hamra, Ishbilya and Vinnell compounds in eastern Riyadh, where many Westerners live.

Cars and pick-up trucks with badly twisted and still smoldering frames littered the three compounds, which housed villas and four-story blocks. Many balconies were blown off, their truncated steel girders jutting out. The bombs also gouged massive holes in many walls and brought down roofs, destroying water storage tanks.

The first explosion at the Al-Hamra residential compound was so strong that it blew out windows a kilometer and a half away, residents said. The blast scoured out a five-meter (17-foot) deep crater, devastating dozens of the 280-odd luxury villas in the sprawling estate and damaging virtually all the rest, witnesses said.

Saudi Television showed daylight footage of the third blast site — a group of low-rise blocks surrounded by piles of debris. The explosion blew a large crater in the pavement in front of buildings with their facades blown away.

A clock in a large hall inside one building had stopped at 11:28, the time of night most witnesses said they had heard the apparently simultaneous explosions. The Interior Ministry said 10 residents of Al-Hamra compound were killed — two Jordanians, four Saudis, two Filipinos, a Lebanese and a Swiss. In Ishbilya compound there were two Saudi victims. The seven Americans were killed in Vinnell compound, which also saw the death of a Saudi.

Mohammed Al-Blaihed, 35, the son of Abdullah Al-Blaihed, undersecretary at the Riyadh governorate, was among the three Saudis killed in the Al-Hamra attack.

A spokeswoman for Australia’s Department of Foreign Affairs and Trade said an Australian man died and a second was wounded in the attacks. “We’ve learned that a 39-year-old man from Sydney has sadly been killed in the attack,” she said.

US officials gave widely varying figures yesterday. Vice President Dick Cheney said earlier that “some 91 people were killed,” according to a Reuters report.

State Department spokesman Philip Reeker said he too had seen that figure reported, but added: “That (91) is one estimate that has been put out there. I have seen it in a number of reports,” Reuters quoted him as saying.

Residents said in addition to the car bomb, the charred bodies of four armed men were found in another vehicle, which also rammed through the gate. They said that further shooting had been heard after the blast.

The ministry spokesman confirmed that there was an exchange of gunfire between security forces — who were present at the compounds — and the terrorists.

According to unconfirmed reports, the attackers shot and killed at least one guard to get through the main gate of the well-guarded compound, hard by the junction of the airport highway and the main motorway to the oil fields in the east of the Kingdom where many expatriates work.

They drove at least one car — three according to some reports — into the compound before detonating their massive cargo of explosives.

The third compound targeted, Al-Jadawel, is one of Riyadh’s newest luxury estates, consisting of about 600 villas and ancillary buildings. Like Al-Hamra, it has 24-hour security protection.

The attackers forced open the main gate and after getting inside they detonated their carload of explosives.

Riyadh’s expatriate housing estates all have round-the-clock security and strangers are not allowed to enter, but that proved no bar to determined militants willing to die themselves.

According to the Spanish Foreign Ministry in Madrid, a Spanish national of Venezuelan origin was also hurt. He was reported to have lived in the kingdom for several years.

The Dutch Foreign Ministry says three of its nationals were injured, one severely, in the bombings.

All three are in hospital and one is in intensive care.