A Palestinian group told a UN panel on Monday it had been subject to threats and “mafia methods” during a campaign of harassment by Israel to silence organisations documenting alleged human rights offences.
Israel dismissed the process overseen by the panel as a sham while declining to comment on the specific allegations.
The independent Commission of Inquiry, established by the UN's Human Rights Council last year, plans to hold five days of hearings, which will be impartial and examine the allegations of both Israelis and Palestinians.
In the opening session, the commission heard from representatives of Palestinian organisations that were shut down by Israel in August and designated as “terrorist” entities.
Shawan Jabarin, general director of human rights group Al Haq, denied the terrorism charge and called the closures an “arbitrary decision”, saying Israeli security forces had used “mafia methods” against it in a years-long harassment campaign.
“They used all means, I can say. They used financial means, they used a smear campaign, they used threats,” he said.
He said his office was sealed with a metal door on August 18.
Asked to detail the threats mentioned to the panel, Mr Jabarin said after the hearing that he had received a phone call from somebody he identified as being from “Shabak”, or the Israel Security Agency, two days after the raid.
The person threatened him with detention, interrogation or “other means” if he continued his work, he said.
A representative for Israel's diplomatic mission in Geneva declined to comment on the specific evidence. An Israeli foreign ministry representative also declined to comment.
“This [inquiry] and the convening of these sham trials shame and undermine the Human Rights Council,” it said in an earlier statement, saying the commission had an “anti-Israel” agenda.
A UN human rights office previously dismissed allegations of bias and said Israel had not co-operated with the commission's work.
The first set of hearings will next turn to the killing of the Palestinian-American reporter Shireen Abu Akleh in May.
The UN rights office has said its findings suggest that she was killed by Israeli forces while an Israeli investigation concluded she was probably unintentionally shot by an Israeli soldier.
Neither the hearings nor the UN Human Rights Council have any legal powers. But investigations launched by the council are sometimes used as evidence before national or international courts.
Israel's ally, the US, has criticised the UN Human Rights Council for what it has described as a “chronic bias” against Israel. It quit the body over the issue in 2018 and before rejoining it in 2022.
The three-member commission was created after the 11-day conflict in May last year, during which 250 Palestinians in Gaza and 13 people in Israel died.
The inquiry mandate includes alleged human rights abuses before and after that, and seeks to investigate the root causes of the tension.