A Jordanian has shot at least nine people at a US-funded police training centre in the eastern outskirts of Amman, killing two Americans and a South African.

The shooter, reported to be a captain in the Jordanian police, has yet to be named. Sources say he opened fire in the training centre’s mess hall. The three killed were all military personnel; six others were injured.

Authorities are treating the event as highly significant: King Abdullah II was reported to have gone to the training centre once news of the attack emerged.

Jordan has long positioned itself as the regional face of moderate Islam and a leader in the fight against terrorism, and is the sole remaining Arab state in coalition against Isis.

The country hosts a robust British, US and French military presence, including military trainers focused on supporting the moderate Syrian opposition through a supply line that runs from Amman across the Syrian border, just 100km to the north.

Despite the government’s pro-western and moderate stance, at street level some Jordanians are known to hold sympathies with the Nusra Front and Isis jihadist terrorists. A robust intelligence and security apparatus has so far prevented violence on today’s scale.

The suspect’s motives are not known, but the timing of the attack has significance for Jordanians: today is the tenth anniversary of a spate of suicide attacks by Al Qaeda that targeted three Amman hotels. Sixty people were killed and 115 injured in the attacks, one of them on a wedding celebration.

One would-be suicide bomber survived after her vest failed to detonate. Sajida al-Rishawi was hanged in February this year in revenge for Isis’s killing of the Jordanian Air Force pilot Moaz al-Kasasbeh, who was burned to death by militants.

On Sunday a Jordanian government spokesman praised the nation for its strength and resilience in the fight against terror, noting that the “black agenda” of the terrorists and their “cowardly methods” have been exposed to the world.