"In an audio speech delivered by its leader, Qassim al-Rimi, (AQAP) claimed credit for the December 2019 Naval Air Station Pensacola attack," SITE, which tracks jihadist media, said in a statement.

The December 6 shooting in a classroom building at the naval base also wounded eight other people, including two responding sheriff's deputies, before police shot dead the assailant.

The FBI formally identified the attacker as Mohammed Alshamrani, 21, a second lieutenant in the Royal Saudi Air Force and a student naval flight officer.

The SITE monitor said he had posted a short manifesto on Twitter prior to the attack that read: "I'm against evil, and America as a whole has turned into a nation of evil."

"I hate you because every day you (are) supporting, funding and committing crimes not only against Muslims but also humanity."

The Twitter account that posted the manifesto -- which also condemned US support for Israel and included a quote from Al-Qaeda's deceased leader Osama bin Laden -- has been suspended.

Saudi Arabia's King Salman was quick to denounce the shooting as a "heinous crime" and said the gunman "does not represent the Saudi people."

Naval Air Station Pensacola hosts the US Navy's foreign military training programmes, established in 1985 specifically for Saudi students before being expanded to other nationalities.

The shooting threatened a programme crucial to the US-Saudi relationship, which involves billions of dollars of military sales to the kingdom.

Around 850 Saudis are among the 5,000 foreign military personnel being trained in the United States.

Last month, however, the US Justice Department said it would send home 21 Saudi military trainees after an investigation into the attack, with Attorney General Bill Barr calling it an "act of terrorism".

The attorney general said 21 of Alshamrani's colleagues were being expelled from the base's flight school after the probe found many of them were in possession of jihadist material and child pornography.

While the material did not warrant criminal prosecution, Barr said Riyadh had "determined that this material demonstrated conduct unbecoming an officer in the Saudi Royal Air Force and Royal Navy," adding that the 21 cadets had been struck from their programme.

He added that the Saudi government had said it would review each case under its code of military justice and criminal code.