WASHINGTON — A US federal judge sentenced a former Blackwater security guard on Monday to 30 months in prison for shooting and killing an Afghan citizen in 2009.

The judge also ordered 29-year-old Justin Cannon to serve two years of supervised release after his prison term ends.

Cannon and a second Blackwater guard, Christopher Drotleff, 31, were convicted of involuntary manslaughter in the May 5, 2009 shooting of Romal Mohammad Naiem, an unarmed Afghan civilian.

Drotleff was sentenced to three years and one month in prison on June 14.

"Justin Cannon opened fire with an AK-47 at the rear of a retreating vehicle and took the life of an innocent Afghan," said US Attorney Neil MacBride.

"While Mr. Cannon was in Afghanistan to support U.S. troops, his incredibly reckless behavior instead undermined our military mission and weakened the bond of trust with the Afghans," MacBride said.

Both Cannon and Drotleff were accused of leaving their military base without authorization to transport local interpreters.

After the the lead vehicle in their convoy crashed during the nighttime outing and overturned on its side, they firing several multiple shots at a passing car, killing Naiem, who was a passenger in the car, and injuring the car's driver.

Another Afghan man walking his dog in the area was also fatally shot. Both Drotleff and Cannon were acquitted of charges in his death and the shooting of the driver.

Blackwater was renamed Xe after it was caught up in several scandals in Iraq, in particular the deaths of between 14 and 17 civilians in Baghdad in September 2007.