Three US services personnel have been killed in a shooting outside a military base in southern Jordan, officials said.

A US official in Washington said one died at the scene and two died in hospital in Amman, the Jordanian capital.

Jordan is a key US ally and member of the US-led military coalition fighting Islamic State, which controls parts of neighbouring Iraq and Syria.

Shots were fired as a car carrying the Americans tried to enter the al-Jafr base near the town of Mann at about noon local time on Friday, military officials in the US and Jordan said.

An American official said the US government is working with Jordanian government figures to gather additional details.

In addition to the US casualties, a Jordanian officer was also wounded, Jordanian officials said.

It was not immediately clear what prompted the shooting.

Jordan faces homegrown extremism, with hundreds of Jordanians fighting alongside IS militants in Iraq and Syria and several thousand more supporting the extremist group in the kingdom.

Last November, a Jordanian police captain opened fire in an international police training facility, killing two Americans and three others. The government subsequently portrayed the police captain as troubled.

The US has spent millions of dollars to help the kingdom fortify its borders. For the West, any sign of instability in Jordan would be of great concern.