US lawmakers have called for a halt to a Saudi military training programme after a shooting rampage at a naval base in Florida in which a Saudi officer killed three American sailors.

Alshamrani, a 21-year-old second lieutenant in the Saudi Royal Air Force, opened fire in a classroom on Friday, killing the three sailors and wounding eight other people before being shot dead by police.

Alshamrani, who was armed with a lawfully purchased Glock 9mm handgun, was reported to have posted a manifesto on Twitter before the shooting denouncing America as “a nation of evil.” The FBI said Sunday they were investigating with the “presumption” it was an act of terrorism, as in most active shooter probes, but had yet to make a final determination.

White House National Security Advisor Robert O’Brien went further, however, saying: “To me, it appears to be a terrorist attack.” “We’ll have to see what the FBI investigation shows,” O’Brien added, on CBS’s “Face the Nation.”The FBI’s main goal, special agent-in-charge Rachel Rojas told a news conference, is to confirm whether Alshamrani “acted alone or was he a part of a larger network.” “We currently assess there was one gunman who perpetrated this attack and no arrests have been made in this case,” she said.

US media also reported that Alshamrani had shown mass shooting videos at a dinner party the night before the attack.Rojas said a number of Saudi students who were close to Alshamrani were cooperating with investigators, and the Saudi government had pledged to “fully cooperate” with the investigation.

The attack has struck a nerve in the United States with its echoes of the September 11, 2001 attacks, in which Saudi citizens accounted for 15 of the 19 hijackers that flew airliners into the World Trade Center and the Pentagon.

Saudi Arabia remains one of the closest US allies in the Middle East, and President Donald Trump has cultivated its controversial de facto ruler, Crown Prince Mohammed bin Salman.