Riyadh: A gunman shot dead one American and wounded another at a petrol station in the Saudi capital on Tuesday, in a rare attack on Westerners in the kingdom, police said.
The victims worked for Vinnell Arabia, a US-Saudi joint venture which provides training for the Saudi Arabian National Guard.
US State Department spokesperson Jen Psaki confirmed the incident and said the second American was "lightly injured".
Following the attack near King Fahd football stadium, a shootout occurred between the gunman and security forces, a police spokesman said in a statement carried by the official SPA news agency.
The assailant was wounded and subsequently arrested, police said, adding: "We heard that he's a Saudi national born in the US."
Police said they did not yet know if the incident could be described as a "terrorist" attack.
Two circles of blood, about the size of a hand, stained the ground at the petrol station about 1.5 metres from the pumps, an AFP photographer said.
Children showed off a small-calibre cartridge case which they said they found in the same area.
Four police jeeps were stationed on the multi-lane road outside the closed petrol station, within sight of the football stadium.
Today's shooting was the first deadly attack on Westerners in Saudi Arabia since several were killed in a wave of al Qaeda violence between 2003 and 2006.
It comes as Saudi Arabia participates in a US-led campaign of air strikes against jihadists of the Islamic State jihadist group (IS) in Syria.
But there was no immediate indication of any links between the attack and the more than three-week-old campaign.
Saudi pilots who participated in the initial late-September strikes against IS received online death threats.
Vinnell Arabia's Facebook page says the firm is "dedicated to providing the best in military training, logistics and support" to the Saudi National Guard, using expertise from former US military and government personnel.
In January, a Saudi court sentenced to death an al Qaeda militant and jailed 10 others over a May 2004 attack that killed six Westerners and a policeman.
The defendants, seven of them brothers, were convicted of aiding assailants who attacked a US company in the northwestern port town of Yanbu, killing two Americans, two Britons, an Australian and a Canadian, as well as a Saudi.