A UN team investigating possible war crimes in Gaza, led by Richard Goldstone, has arrived in the Strip on a week-long fact finding mission.
The four-member team entered from Egypt after Israel failed to grant visas, despite repeated requests by the UN.
The UN wants to investigate whether Israel and Hamas committed war crimes during Israel's three-week operation in Gaza in December and January.
Israel accuses the UN branch carrying out the mission of bias against it.
The UN Human Rights Council has been accused of singling out Israel unfairly, and is viewed by some as having less credibility than other parts of the United Nations.
But correspondents say the selection of Mr Goldstone, a respected South African war crimes prosecutor who is also Jewish, as head of the inquiry has given it greater clout.
"They have been instructed to prove that Israel is guilty and we will not collaborate with such a masquerade," foreign ministry spokesman Yigal Palmor told AP news agency.
Public hearings
The team plans to meet "all concerned parties", including non-governmental organisations, UN agencies and victims and witnesses of alleged violations of international humanitarian law, its office said in a statement.
Mr Goldstone has previously said his team had hoped to visit southern Israeli towns which have suffered Palestinian rocket fire , before entering Gaza from Israel, but Israel has shown no sign of allowing access.
Israel was initially angered that the team was tasked only with investigating alleged Israeli violations, but after Mr Goldstone was appointed, its mandate was widened to cover the activities of Palestinian militants too.
Inquiry conclusions
Several investigations into alleged violations of international law during Israel's 22-day operation in Gaza, which ended on 18 January, have now reported back.
UN Secretary General Ban Ki-moon has requested more than $11m (£7m) compensation from Israel for damage to UN property in Gaza, after a limited UN inquiry accused Israel of targeting known civilian shelters and providing untrue statements to justify actions in which civilians were killed.
The report found Israel to blame in six out of nine incidents when death or injury were caused to people sheltering at UN property and UN buildings were damaged.
The Israeli military has concluded in an internal investigation that its troops fought lawfully, although errors did take place, such as the deaths of 21 people in a wrongly targeted house.
Meanwhile, a fact-finding team commissioned by the Arab League said there was sufficient evidence for the Israeli military to be prosecuted for war crimes and crimes against humanity, and that "the Israeli political leadership was also responsible for such crimes".
It also said Palestinian militants were guilty of war crimes in their use of indiscriminate attacks on civilians.
Palestinian rights groups say more than 1,400 Palestinians were killed during the January conflict. Israel puts the figure at 1,166.
Israeli and Palestinian estimates also differ on the numbers of civilian casualties.
Ten Israeli soldiers were killed, including four by friendly fire, and three Israel civilians died in rocket attacks by Palestinian militants.