The official Saudi Press Agency says a gunman has killed an American citizen and wounded another at a gas station in Saudi Arabia's capital.

A Riyadh police spokesman was quoted by SPA as saying Saudi security forces tracked down the gunman and exchanged fire with him, before wounding and arresting him. The gunman was not identified.

It was not immediately clear if the attack was related to terrorism.

The agency reported that the police spokesman, who was not identified, said the mid-afternoon attack occurred while the Americans were inside a vehicle at a gas station in the eastern part of the capital.

Saudi Arabia was hit by a wave of al-Qaida attacks around a decade ago that targeted security forces and foreigners.