Security has been stepped up
outside of expatriate compounds
since last week's attacks
The arrest came a week after three suicide bombers detonated explosives outside of expatriate compounds in Riyadh, killing at least 34 people.
A US official said the gunman was detained at 6:00 am without giving further details.
A State Department official in Washington said an “armed visitor” was arrested at the outer gate of the consulate.
The consulate closed for the public for the rest of the day and the “incident” was under investigation.
Saudi Arabia said it had arrested four people linked to the triple suicide attacks and identified five of the perpetrators.
Saudi Interior Minister Prince Nayef Bin Abdul Aziz said the four detainees were members of Al-Qaeda.