Early reports indicate that three explosions struck the Al-Hamra, Cordoval and Gedawal compounds, located in eastern Riyadh. Hospitals in Riyadh reported that more than 60 injured had already been received, at least 40 of whom were US citizens.

'The three explosions that occurred in eastern Riyadh were suicide bombings [ -] set off by cars stuffed with explosives that were driven into the targeted compounds,' Saudi Interior Minister Prince Nayef bin Abdulaziz said.

A fourth bomb detonated at the headquarters of the American-Saudi-owned Saudi Maintenance Company, also known as Siyanco.

A US foreign ministry spokesperson on Tuesday said that Colin Powell's visit to the kingdom would go ahead as scheduled. Powell himself, on a tour in the Middle East to gain Arab support for a US-sponsored Israeli-Palestinian peace plan, said in Jordan that the bombings bore all the hallmarks of the Al-Qaeda network of Saudi-born Osama BinLadin.

'Once again it reminds us that terrorism is a global phenomenon,' Powell said. 'It is just part of Al-Qaeda and other terrorist organisations' willingness to kill innocent people in order to push forward a criminal agenda.'

In recent months there have been several attacks against Western targets in the kingdom. In late February a UK national was shot in Riyadh, while several others were targeted in drive-by shootings and car bombings.