By Angus McDowall
RIYADH (Reuters) - A Saudi Arabian gunman killed a U.S. national and wounded another in the capital Riyadh on Tuesday, officials said, heightening Western concerns over security in the world's top oil exporter as regional unrest rises.
Police later shot and wounded an assailant and then arrested him, said a statement from the police carried by state media. No motive for the attack was given, but a source familiar with the situation said the gunman may have been taking revenge after being sacked from his job.
"The attack resulted in the killing of one person and wounding another and it turned out they were of American citizenship," the police statement said.
Interior Ministry spokesman Major General Mansour Turki said an investigation was under way into what appeared to be the first killing of a Westerner in Saudi Arabia in years.
The source familiar with the situation said the assailant had recently been dismissed from his job and believed that one of the victims had been responsible for his firing.
The Americans worked for Vinnell Arabia, a local affiliate of U.S. defense company Northrop Grumman Corporation which provides training and support services to the Saudi Arabian National Guard, U.S. State Department spokeswoman Jen Psaki said.
"We can confirm that two U.S. citizen employees from Vinnell Arabia, a U.S. defense contractor supporting Saudi National Guard military programs in Riyadh, were shot at a local gas station/store approximately 0.5 miles from the Vinnell Arabia base in Riyadh, which is located approximately 20 miles from the U.S. Embassy," Psaki said.
The official added that the U.S. government was evaluating its security and would take steps to ensure the safety of all U.S. mission personnel.
With tensions in the region heightened due to conflicts in Syria and Iraq, and with Saudi officials concerned about rising domestic militancy, security at Western compounds is being stepped up.
"We will be heightening security around our compound," said the manager of a Western residential compound in Riyadh.
Most security at Western compounds has been provided by the Saudi Arabian National Guard since a string of attacks on foreign targets a decade ago.
Police said Tuesday's attack happened when the two Americans stopped their vehicle at a filling station in an eastern district of the capital. Turki said that a third U.S. national in a different vehicle had witnessed the attack.
"That area would be on my way to work and I'm in that area often stopping at local shops and buying things. I might avoid stopping there for a while," said one U.S. national living in Riyadh.
An Italian working in the oil industry in Saudi Arabia said: "The targets are Americans not really any others, so I'm not too concerned. But I did think about posting a few bumper stickers with the Saudi flag and Allah Akbar (God is Great) on my car."
Saudi officials have said this year they are concerned about a rise in domestic Islamist militancy due to the conflicts in Iraq and Syria. The government has decreed tough penalties for terrorist crimes.
The last reported killings of Westerners by armed assailants in Saudi Arabia happened in 2007 when three French nationals were shot dead while camping in the northwest of the country.
A group of men accused of belonging to al Qaeda are on trial in Riyadh for those killings and are awaiting a verdict.
From 2003 to 2006, al Qaeda carried out a series of attacks on foreign and government targets that killed hundreds, before being crushed by Saudi security forces.
(Additional reporting by Amena Bakr in Doha and Warren Strobel in Washington; Editing by William Maclean and Robin Pomeroy)