Both Israel and Palestinian militant groups committed war crimes and acts that were likely crimes against humanity during the fighting in the Gaza Strip earlier this year, a United Nations fact-finding mission concluded Tuesday.

In a 547-page report, the mission said both Israeli and Palestinian authorities must engage in "good faith, independent roceedings" to investigate their own sides within six months, or the UN Security Council should refer the case to the International Criminal Court's prosecutor in The Hague.

The mission was headed by the former chief prosecutor of the international courts for Yugoslavia and Rwanda, Richard Goldstone, and comprised three other experts in various fields, including international law and weapons.

"We live in a world today were there is accountability for war crimes," Goldstone said. "This is a very new situation."

Israel refused to cooperate with the mission because it regarded it as having biased instructions from the UN Human Rights Council, which it says has a track record of repeatedly singling out Israel for criticism and turning a blind eye to any Palestinian wrongdoing.

The foreign ministry in Jerusalem said it would "read the report carefully," and added that the military had already carried out investigations into over 100 cases of alleged abuse.

Goldstone said at a press conference that the Palestinians have not looked into their actions at all, and the report concluded that Israel to date "has not carried out any credible investigations into alleged violations."

The former South African justice cited longstanding ties to Israel and his Jewish background, calling allegations he was anti-Israel "ridiculous." He said the parties to the conflict stand to benefit from impartial investigations.

While the report - based on nearly 200 interviews and over 20,000 pages of documents and photos - determined that violations of international law had been committed, Goldstone declined to name individuals on either side, saying that was for a prosecutor to decide.

Israel, the mission wrote, should pay compensation to Palestinians who suffered losses or damages as a result of any unlawful actions by the military.

During the conflict, which started on 27 December 2008 and lasted three weeks, human-rights groups say approximately 1,400 Palestinians were killed, mostly civilians, along with Israeli fatalities of three civilians and 10 soldiers.

The mission believed the Israeli military operation was "directed at the people of Gaza as a whole" to "punish" the population. It cited incidents where food productions facilities, drinking water installations and other such sites were attacked, saying these might be "crimes against humanity."

The report also condemned the Israeli blockade on the Gaza Strip, which it deemed "collective punishment" that was part of a "systematic policy" to isolate the coastal territory.

Investigations, the report said, led the team to believe human shields were used in certain cases, hospitals were attacked and civilians were shot while carrying white flags.

On the other side, Palestinian rocket fire into southern Israel constituted "war crimes and may amount to crimes against humanity" as the militants failed to distinguish between civilians and soldiers, causing "terror."

In an aside, the report said Israel failed to protect its Arab citizens against the rocket fire in the same way that it protected its Jewish residents.

Israel has said the rocket fire from Gaza into its territory was the reason it launched the military operation and that it was not aimed against the Palestinian population.

The report also noted internecine Palestinian violence during the war, including extra-judicial executions and arbitrary arrests.

Goldstone called on the militants to release Gilad Shalit, an Israeli soldier captured in 2006, and said Israel should cease holding Palestinian political prisoners.

The mission would present its report to the UN Human Rights Council later this month in Geneva, where a heated debate is expected.

The Jerusalem-based NGO Monitor earlier this month casted doubt as to the neutrality of the Goldstone Commission on Gaza.

Goldstone said in July he regards the mandate of the fact-finding mission as requiring an independent investigation into all alleged violations of international humanitarian law and international human rights law during the IDF's 22-day offensive.

"The testimonies we have heard from victims and witnesses... have been very difficult to hear, but I believe it is important that we listen to these stories," said Goldstone.

In response to the report released on Tuesday, Israel's Foreign Ministry said it was "appalled and disappointed," particularly by the comparison of Hamas to Israel.

"The UN body has dealt a huge blow to governments seeking to defend their citizens from terror," said Foreign Ministry spokesman Yigal Palmor.