Israel refused to accept the findings of a highly critical UN inquiry into the Gaza war and said today it would launch a diplomatic offensive to prevent any risk of prosecutions.

No independent inquiry into the military's conduct during the war last January would be held, a clear rejection of one primary recommendation from the UN report.

The inquiry, headed by a former South African judge, Richard Goldstone, delivered a detailed and damning criticism of the war, accusing both Israel and armed Palestinian groups, notably Hamas, of war crimes and possible crimes against humanity. It was by far the most serious international inquiry into the three-week war, which left 1,400 Palestinians and 13 Israelis dead and which triggered a wave of criticism across the world.

"This report was conceived in sin and is the product of a union between propaganda and bias," said Mark Regev, spokesman for the Israeli prime minister, Binyamin Netanyahu. "Israel is a country with a fiercely independent judiciary … Everything done by the military in Israel is open to judicial review by the independent judiciary."

Israel had refused to co-operate with the inquiry, not letting the team enter Israel or the occupied West Bank. It said the UN human rights council, which commissioned the inquiry, was biased against Israel.

"The mandate was biased from the beginning and it would have been a mistake to give credibility to a mission that has more in common with a kangaroo court than it does with a serious investigation," Regev said.

For its part, Hamas also rejected the criticism. "The Palestinian people and the Palestinian resistance were in a position of self-defence and not of attack. One cannot compare the simple capabilities of the resistance with the great strength of the occupation," said Ismail Haniyeh, a Hamas leader and former Palestinian prime minister.

After the inquiry was published yesterday evening, a legal team from Israel's foreign ministry met with other government officials to prepare an analysis of the UN report. Netanyahu reportedly held meetings into the night on the impact of the findings.

Israel is concerned that, when the UN human rights council discusses the report later this month, it could agree to pass it to the UN security council. The security council could then decide to pass the findings on to the international criminal court, where arrest warrants could be issued ahead of prosecutions.

Israel's deputy foreign minister, Danny Ayalon, who is on a visit to Washington, said he would meet the US ambassador to the UN, Susan Rice, to minimise the impact of the report before it reaches the UN security council. Other senior figures from the Israeli government are expected to begin a round of telephone calls with ministers from other governments, particularly the five permanent members of the security council, to head off any decision that might lead to prosecutions. The Ha'aretz newspaper said priority calls would go out to EU nations, in the hope of influencing the debate at the UN human rights council in Geneva.

The 575-page UN report said that Israeli military personnel should face "individual criminal responsibility" for grave breaches of the laws of war. Although critical of both sides, it singled out Israel and its policy towards the Palestinians of Gaza for the most serious condemnation. It accused Israeli troops of using Palestinians as human shields, a war crime, and said the long Israeli economic blockade of Gaza amounted to "collective punishment intentionally inflicted by the government of Israel on the people of the Gaza Strip".

It recommended that the UN security council should require Israel to investigate the allegations raised, and if it failed to do so within six months the case should be passed to the prosecutor of the international criminal court. Each country that is a high contracting party to the Geneva conventions had a duty to search for and prosecute those responsible, it said.

The inquiry rejected Israel's argument that the war was a response to Palestinian rocket fire and therefore an act of self-defence. Instead, it found the war was "a deliberately disproportionate attack designed to punish, humiliate and terrorise a civilian population". Israeli actions depriving Gazans of means of subsistence, employment, housing and water, and denying their freedom of movement "could lead a competent court to find that the crime of persecution, a crime against humanity, had been committed", it said.

But the inquiry also condemned Hamas. It said Palestinian rocket attacks did not distinguish between civilian and military targets, caused terror among Israeli civilians and "would constitute war crimes and may amount to crimes against humanity". Gazan security forces – controlled by Hamas – carried out extrajudicial executions and the arbitrary arrest, detention and ill-treatment of people, especially political opponents. It also called for the release of Gilad Shalit, an Israeli soldier held captive in Gaza for more than three years.