Monday's first bombing, near the US consulate in Jeddah, was carried out not by a Saudi but by a "resident foreigner," General Mansour al-Turki, the interior ministry spokesman, told Al-Arabiya.

Turki told state Al-Ekhbaria news channel that the suspect, in his 30s, was closer to a mosque in the area than to the American consulate.

"Investigations (are) ongoing to find out the goals and motives of the bomber," said Turki.

He also said on the news channel's Twitter account that "devices that failed to explode (were) found in the vicinity of the site".

The American embassy in Riyadh reported no injuries among US consulate staff.