Jerusalem (CNN) -- Israel's deadly raid on an aid flotilla that attempted to run the blockade of Gaza was "regrettable" but legal under international law, an independent Israeli commission reported Sunday.

The commission, led by retired judge Yaakov Turkel, found that Israeli commandos "acted professionally and in a measured manner in the face of unanticipated violence" when they seized the Gaza-bound aid ship Mavi Marmara. Members of the Turkish relief group IHH "were direct participants in hostilities" who attacked the Israeli troops, the commission reported.

"The actions carried out by Israel on May 31, 2010, to enforce the naval blockade had the regrettable consequences of the loss of human life and physical injuries," the report concludes. "Nonetheless, and despite the limited number of uses of force for which we could not reach a conclusion, the actions taken were found to be legal pursuant to the rules of international law."

Nine people were killed when Israeli forces boarded the Mavi Marmara and its accompanying convoy in international waters in May. Kevin Ovenden, a survivor of the raid, called Sunday's report a "whitewash" and a "sick joke."

"It is simply unfeasible to claim that, for example, the two men shot immediately to the left and right of me were gunned down in some act of self-defense," Ovenden, a representative of the British aid group Viva Palestina, said in a written statement. "They were shot from above. No Israeli commando was in sight of us when the bullets rang out."

Palestinian leaders also criticized the report on Sunday.

"The Turkel commission does not have the credibility necessarily because it was formed by the Israeli government, which is the party accused of the crime against the civilians in international waters," said Palestinian government spokesman Ghassan Khatib.

"Only an international investigation committee has the right to investigate that Israeli crime, because Israel can not be the criminal and judge at the same time," he said.

The raid strained ties between Israel and Turkey, its strongest ally among Muslim nations, and triggered a wave of international condemnation of Israel and its policies toward Gaza. But the controversy led Israel to loosen its embargo on the territory, allowing more civilian goods and construction materials to flow in while still banning military equipment and weapons.

In September, the U.N. Human Rights Council found Israeli forces "committed serious violations of international law" in the raid and suggested that six of the civilians deaths were "consistent with ... an arbitrary and summary execution." Israel called the report "as biased and as one-sided as the body that has produced it."

Gaza is ruled by the Islamic militant group Hamas, which refuses to recognize Israel's right to exist and has been branded a terrorist organization by the United States and the European Union. The Turkel Commission found that the blockade "was lawful and complied with the rules of international law," but human rights groups have condemned the closure as an unlawful collective punishment of Palestinian civilians.

The Israeli human rights group Gisha, which advocates for Palestinians, said the continued blockade still restricts Palestinian trade and movement "with no valid security justification."

"Gisha expresses hope that Israel will cancel the many remaining restrictions that are not related to concrete security risks and will allow the free movement of people and goods into and out of Gaza, subject only to individual security checks," it said.

And in a statement in response to Sunday's report, Turkey called the continuing blockade "devoid of legal basis and legitimacy."

The Turkish commission that investigated the raid said it was "surprised, appalled and dismayed" by the Israeli findings.

"While it had the possibility of intercepting the convoy carrying unarmed civilians without causing bloodshed, Israel opted for a course which made loss of life inevitable," the commission said in a written statement. And instead of rethinking their tactics when passengers began to resist, the Israelis decided "to attack with increased violence," it said.

"The result is self-evident and requires no further explanation," the Turkish commissioners said.

Turkey withdrew its ambassador to Israel after the raid and has said it won't resume normal diplomatic ties with the Jewish state without an apology and compensation for the victims' families.

Some Jewish organizations, meanwhile, praised Sunday's report.

"The report fully and completely upholds the legality of the decision taken by the Israeli government to establish the naval blockade of Gaza and vindicates Israel's actions in self-defense as it stopped the flotilla," said Anti-Defamation League national director Abraham H. Foxman in a statement.

"The Israeli government and the IDF took the investigation seriously and offered their full cooperation, showing Israel's commitment to transparency and military accountability under the law," Foxman said, referring to the Israeli Defence Force.

Israeli officials have said their boarding party was attacked with knives, metal poles and other objects. Sunday's report says two were shot, one in the knee and one in the stomach. The Turkel Commission found that of 133 cases where Israeli troops used force, 127 were in accordance with international law and no conclusions could be reached in the rest.

Sunday's report was the first of two parts. The second will be presented later on in the year and will look into the decision-making process that led to the attack on the flotilla.

Sarah Colborne, director of the Palestine Solidarity Campaign, who was on board the Mavi Marmara when the Israeli Defence Force attacked the boat, said:

"However hard the Israeli Government attempt to rewrite history, they can't rewrite the truth. The facts are simple, the Mavi Marmara was carrying essential humanitarian aid like baby milk to the besieged people of Gaza. There were no guns or weapons on board the boat, we were in international waters, when over 300 bullets -- or one for every two people on board -- rained down on us, killing 9 people and injuring over 50."

"The actions of the Israeli Defence Force and the Israeli Government were by all international standards of law illegal as is their continued occupation of Gaza and the oppression of the Palestinian people."

CNN's Kareem Khadder, Shira Medding and Ivan Watson contributed to this report