The United Nations rights chief on Friday urged Israeli forces to stop using excessive force against Palestinian protesters and called for troops who have committed abuses "to be held accountable"."Every week, we witness instances of use of lethal force against unarmed demonstrators," the UN High Commissioner for Human Rights, Zeid Ra'ad Al Hussein, said in a statement. "Warnings by the United Nations and others have seemingly gone unheeded, as the approach of the security forces from week to week does not seem to have changed," he added. Forty-two Palestinians have been killed by Israeli fire since March 30, according to the UN. Most of the Palestinians killed by Israel since the start of "March of Return" protests were shot by snipers on the border, while a few others were killed by Israeli artillery or air strikes.No Israelis have been injured.Live ammunition "The staggering number of injuries caused by live ammunition only confirms the sense that excessive force has been used against demonstrators - not once, not twice, but repeatedly," Zeid said. "It is difficult to see how children, even those throwing stones, can present a threat of imminent death or serious injury to heavily protected security force personnel," he added. The Israeli army says its troops only open fire in self-defence or to stop protesters attempting to breach the barrier separating the territory from Israel.The return march protests are calling for millions of Palestinians to be allowed to return to their historic homes, that are now inside Israel.Israel says such a return would destroy its identity as a Jewish state and accuses Hamas of seeking to use the protests as a means of violence.