The UN condemned the "gruesome" killing of a wounded alleged Palestinian attacker by an Israeli soldier in the West Bank, after a video of the shooting spread widely online.

"I strongly condemn yesterday's apparent extra-judicial execution of a Palestinian assailant in Hebron in the occupied West Bank," UN Special Coordinator for the Middle East peace process Nickolay Mladenov said in a statement assailant.

"This was a gruesome, immoral and unjust act that can only fuel more violence and escalate an already volatile situation."

He welcomed, however, Israeli Defence Minister Moshe Yaalon's condemnation of the incident and called on the Israeli authorities to "swiftly bring to justice" the alleged perpetrator.

The Israeli army on Thursday arrested a soldier caught on video shooting a wounded alleged Palestinian attacker in the head as he lay on the ground after stabbing another soldier, his knife lying beyond his reach.

The clip, which was widely shared online and shown by state-owned and commercial Israeli TV channels, shows what appears to be one of the most flagrant cases of Israeli forces' alleged use of excessive force so far in the wave of Israeli-Palestinian violence that erupted in October.

The incident was immediately condemned as an "execution" by Israeli rights group B'Tselem and as a "war crime" by Palestinians.

'Detained on suspicion murder'

A military spokesman said the soldier was being "detained on suspicion murder," with his remand extended to Tuesday.

The soldier had not been at the actual site of stabbing attack, but arrived some six minutes later, according to a preliminary after action review.

Three officers on the scene were also reprimanded for not treating the wounded Palestinian, a military spokesman said, noting that in the past six months some 170 Palestinians wounded during attacks or attempted attacks received medical treatment from army forces.

Military chief of staff Lieutenant General Gadi Eisenkot said on Friday that the army gives its soldiers "full support in the case of errors, but not over conduct that is not normative and goes against the army's values."

Israeli Prime Minister Benjamin Netanyahu said the soldier's behaviour was not in keeping with the army's values and Yaalon vowed the shooting was being treated with "utmost severity".

In pictures: A decade of anti-wall struggle

Since October 1, Israeli forces or settlers have killed 206 Palestinians, including protesters, bystanders and attackers, at least 57 of them from Hebron.

Meanwhile, Palestinian attackers have killed at least 29 Israelis, mostly in stabbing attacks.

The surge in violence erupted in Jerusalem in October after an increase of Israeli incursions into the al-Aqsa Mosque compound, Islam's holiest site outside Saudi Arabia.