BEIRUT, Lebanon — Two American employees of a United States military contractor were shot on Tuesday, one fatally, by a recently dismissed Saudi-American colleague at a gas station in Riyadh, the Saudi capital, the Interior Ministry reported.

The shooting, which appeared to be workplace-related, came amid heightened concern about possible reprisal attacks by Islamic militants against the United States and Saudi Arabia, which are collaborating in a military coalition against the Islamic State, the extremist group that has seized parts of Syria and Iraq.

Saudi security forces rushed to the scene of the shooting, where they exchanged fire with the gunman before wounding him and taking him into custody, American and Saudi officials said.

The Saudi Embassy in Washington released a statement from the Interior Ministry that identified the assailant as Abdulaziz Fahad Abdulaziz Alrashid, 24, a dual Saudi-American citizen who had been “recently dismissed from his job due to drug-related issues.”