More than a dozen Saudi service members training at U.S. bases will be expelled, a U.S. official confirmed to CBS News' David Martin. The service members are being expelled after an investigation into the deadly December shooting by a Saudi national at Naval Air Station Pensacola.

The service members are not accused of having involvement in the shooting, but some are said to be linked to extremist movements and a number are accused of possessing child pornography.

CNN first reported the news of the Saudi service members' expulsion.

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Secretary of Defense Mark Esper said on "Face the Nation" on Sunday that there has been an investigation by the Department of Justice and FBI into the shooting.

"I've signed out directives that address enhanced screening of all of our foreign students that address credentialing going forward, weapons policies, etc.," Esper told CBS News. "So we're doing everything we can. The investigation is being conducted by DOJ and FBI. I'm sure they will release something on that in the coming days."

A general view of the atmosphere at the Pensacola Naval Air Station following a shooting on December 6, 2019, in Pensacola, Florida. Josh Brasted / Getty

Three people were killed and eight others wounded when a gunman opened fire at Naval Air Station Pensacola on December 6. The 21-year-old suspect, who was also killed, was a member of the Saudi Air Force and an aviation student at the base. The FBI said at the time that they will "work with the presumption that this was an act of terrorism."

The suspect had been in the country since August 2017 to participate in a Saudi Arabia-funded U.S. Air Force Foreign Military Sales training and was scheduled to stay until August 2020. The weapon used in the attack was purchased lawfully.

Following the shooting, the Pentagon grounded Saudi military aviation students at three bases in Florida: Naval Air Station Pensacola, Naval Air Station Whiting Field and Naval Air Station Mayport.