A Saudi- American citizen opened fire at two American contractors, leaving one dead and the other one injured at a gas station of Saudi Arabia's capital Tuesday.

Earlier the shootout raised tremor in the area speculating that it may be a terror strike in retaliation for the US-led efforts against the ISIS. However, investigation ruled out the allegation as shooter's motive for the attack was over drug-related issues, and he's apparently pinpointing to one of the Americans for being dismissed from the job.

Saudi Interior Ministry named the alleged shooter as Abdulaziz Fahad Abdulaziz Alrashid, 24, a previous worker for Vinnell Arabia, a US defense contractor. The shooter sustained some injuries and was detained following a shootout with Saudi Security Forces.

Interior Ministry spokesman Major General Mansour Turki claimed that an investigation led to what appeared to be the first assassination of a Westerner in Saudi Arabia after long years.

The Americans worked for Vinnell Arabia, a local associate of U.S. Defense Company Northrop Grumman Corporation providing training and support services to the Saudi Arabian National Guard, stated U.S. State Department spokeswoman Jen Psaki.

"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 added.

Psaki assured that U.S. government was assessing its security and would be carefully focusing to ensure the security of all U.S. mission personnel. Western compounds security has been tightened especially the growing clashes in Syria and Iraq.

Saudi police reported that the shooting occurred when the two Americans stop by at the eastern district of the capital gas station. Another US national from a different vehicle witnessed the attack but remained unharmed.