The UN expert on the human rights situation in the occupied Palestinian territories resigned Monday, complaining that Israel had never granted him access to areas he is meant to monitor.
"The United Nations Special Rapporteur on the situation of human rights in the Palestinian territories, Makarim Wibisono, today submitted his resignation to the President of the Human Rights Council, effective as of 31 March 2016," a UN statement said.
Wibisono, who took up the independent role in June 2014, "expressed deep regret that, throughout his mandate, Israel failed to grant him access to the Occupied Palestinian Territory", it said.
"Unfortunately, my efforts to help improve the lives of Palestinian victims of violations under the Israeli occupation have been frustrated every step of the way," Wibisono said in the statement.
The Indonesian diplomat said he had been assured before taking up the position that he would have access to the occupied Palestinian territories.
"I took up this mandate with the understanding that Israel would grant me access, as an impartial and objective observer," he said.
But he said repeated requests for access were unsuccessful.
"With no reply from Israel to my latest request, in October 2015, to have access by the end of 2015, it is with deep regret that I accept the premise upon which I took up the mandate, which is to have direct access to the victims in the Occupied Palestinian Territory, will not be fulfilled," he said.
By contrast, the Palestinian government had "cooperated fully" with his mandate.
Israel has long had stormy relations with the UNHRC, which it accuses of having a built-in bias against the Jewish state.
Israel's foreign ministry said Wibisono's mandate was such that "he could not give an unbiased view".
"From the Israeli perspective the dice were loaded from the first day," ministry spokesman Emmanuel Nahshon told AFP.
"The mandate of the rapporteur was written so that it could not do its work in an objective and fair manner, with all the attention directed on the Palestinian side, on the Palestinian narrative and ignoring abuses against Israeli civilians," he added.
In a separate statement, the Israeli foreign ministry challenged the UNHRC's conduct and the "content of its resolutions".
"The Palestinians and their supporters in the Council enjoy an automatic majority leading to a one-sided and discriminatory performance of the Council and its various mechanisms," the statement said, adding that "as long as this state of affairs persists, Israel's attitude will reflect it".
Wibisono took over from American professor Richard Falk, who repeatedly locked horns with Israel, Washington and others over his harsh criticism of the Jewish state, which included a call to boycott companies profiting from its settlement enterprise in the occupied Palestinian territories.
Wibisono has been less controversial, although he harshly criticised the 2014 Gaza war, warning the "ferocity of destruction and high proportion of civilian lives lost in Gaza cast serious doubts over Israel's adherence to international humanitarian law".
And in November, Wibisono accused the Israeli security forces of using excessive force against the Palestinians and said they may have carried out summary executions as they sought to crack down on a wave of lone-wolf attacks with knives, guns and cars.
In Monday's statement, he voiced deep concern over the lack of protection for Palestinians who face an ongoing range of human rights violations.
"I reluctantly wish to pass the baton to a successor, selected by the Human Rights Council," Wibisono said.
"It is my sincere hope that whoever succeeds me will manage to resolve the current impasse, and so reassure the Palestinian people that after nearly half a century of occupation the world has not forgotten their plight and that universal human rights are indeed universal," he added.
He stressed that it was important for Israel's own human rights credibility to cooperate with the mandate and to provide access to the Palestinian territories.