GENEVA - An 18-month prison sentence for an israeli soldier who shot dead a wounded Palestinian assailant is an "unacceptable" punishment for "an apparent extra-judicial killing", the UN said Friday.

United Nations human rights office spokeswoman Ravina Shamdasani further charged the Jewish state with having "a chronic culture of impunity" regarding cases involving israeli troops and Palestinians. In March 2016, israeli Private Elor Azaria was caught on video shooting Palestinian Fattah al-Sharif in the occupied West Bank city of Hebron.

The video showed Sharif, 21, lying wounded on the ground, shot along with another Palestinian after stabbing and wounding a soldier , according to the army. Azaria then shoots Sharif in the head without any apparent provocation. After a months-long trial, Azaria was on Tuesday sentenced to 18 months in prison, with a further 18 months suspended.

"We are deeply disturbed at the lenient sentence ," Shamdasani said. "While the prosecution and conviction are very welcome steps towards accountability, the punishment... is difficult to reconcile with the intentional killing of an unarmed and prone individual," she added.

According to the rights office, more than 200 Palestinians have been killed by israeli security forces in the West Bank since September 2015 and Azaria has been the only one to face trial.

israeli Prime Minister Benjamin Netanyahu on Thursday backed pardoning Azaria.