About a dozen Saudi nationals receiving military training in the U.S. are expected to be expelled in the wake of a Pentagon review of a Saudi officer who opened fire last month at a naval base in Pensacola, Fla., a U.S. official familiar with the investigation confirms to NPR.

The official, who was not authorized to speak publicly about the investigation, said some of the dozen Saudis failed to alert authorities about the Pensacola shooter's warning signs, including that he allegedly showed videos of other mass shootings at cadet dinner parties.

Federal authorities linked some of the Saudi trainees to extremist rhetoric online, the official said.

It is not clear when exactly the students will be kicked out of the country, but federal officials are planning to announce the decision in the coming days.

In December, a Saudi aviation student opened firein a classroom of the naval base, leaving three young sailors dead and wounding eight others.

The incident prompted the Pentagon to suspend operational training of all Saudi Arabian military students in the U.S. indefinitely, as federal investigators conduct a security review of the more than 800 military students in the U.S. from Saudi Arabia.

Some members of Congress used the incident to renew attention to foreign military exchange training programs, which bring thousands of students from dozens of countries to America to be taught at U.S. bases.

Top military officials view the programs as a way to boost relationships with foreign militaries and to increase the sharing of intelligence around the globe as a national security measure.

When asked on Fox News Sunday about the move to kick out a dozen Saudi trainees, National Security Adviser Robert O'Brien said U.S. officials, including Defense Secretary Mark Esper, are exhibiting caution in the aftermath of the bloody rampage.

"I think we're being very careful. Obviously, Pensacola showed that there had been errors in the way that we vetted, and out of an abundance of caution Secretary Esper has taken these actions to protect our service men and women," O'Brien said.

The dozen Saudis set to be expelled from the U.S. are not accused of aiding the 21-year-old Saudi gunman who carried out the attack, according to CNN, which first reported Saturday night that the Saudi servicemen would be removed from the country.

Federal investigators believe the Saudi gunman, who legally purchased a handgun before the shooting, acted alone and was not part of a larger network. A sheriff's deputy shot and a killed him.

Shortly after the shooting, an account linked to the gunman surfaced showing vitriolic posts on social media criticizing American foreign policy and military action, saying the country had become "a nation of evil."

The Department of Justice and the Federal Bureau of Investigation both declined to comment on the pending announcement about the Saudi students being expelled.

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