Two U.S. military personnel have been killed in a gun attack at a police training centre outside Jordan's capital, Amman, security sources say.

A security source told the Reuters news agency the assailant was a Jordanian police officer and that he killed himself after targeting the Americans.

It is not yet clear what prompted his action.

The U.S.-funded facility in Muwaqqar, on Amman's eastern outskirts, is used to train Iraqi and Palestinian officers.