A U.N. panel has concluded that Israel’s armed raid on a flotilla carrying Turkish and other foreign activists and humanitarian supplies to the Gaza Strip last year was legal, but that its use of force in an operation that left nine people dead was “excessive and unreasonable.”

The 105-page report concluded that Israel has a legal right to maintain a naval blockade of Gaza. But it called on the Israeli government to offer a public expression of “regret” for the deaths and injuries on the Mavi Marmara, where the most violent clashes occurred, and to pay compensation to the families of the dead.

The May 2010 raid on the flotilla, which was organized in Turkey, threatened to torpedo the rapprochement between Israel and Turkey, one of the region’s most important Islamic governments and a U.S. ally.

The U.N. report said that the Israeli government had failed to provide a “satisfactory explanation” as to how and why the nine passengers, including one American, were killed in the incident.

“Forensic evidence showing that most of the deceased were shot multiple times, including in the back, or at close range has not been adequately accounted for in the material presented by Israel,” it concluded.

Israel has rejected a Turkish demand that it apologize for the deaths, despite pressure from Washington to do so. The report is scheduled to be released Friday. The New York Times, which obtained a copy of the report, reported the findings Thursday.

U.N. Secretary General Ban Ki-moon established the panel in a bid to help reconcile differing accounts of the incident from Israel and Turkey and to help repair the strained diplomatic relationship between the two countries. The authors of the report were Sir Geoffrey Palmer, a former New Zealand prime minister, and Álvaro Uribe, Colombia’s former president.

The report concluded that “Israel faces a real threat to its security from militant groups in Gaza” and had imposed the naval blockade “as a legitimate security measure” to prevent weapons from entering the strip by sea. Israeli commandos “faced significant, organized and violent resistance from a group of passengers when they boarded the Mavi Marmara, requiring them to use force for their own protection,” the report found.

Still, it said, “Israel’s decision to board the vessels with such substantial force at a great distance from the blockade zone and with no final warning immediately prior to the boarding was excessive and unreasonable. . . . The loss of life and injuries resulting from the use of force by Israeli forces during the takeover of the Mavi Marmara was unacceptable.”

The Israeli government declined to make an official comment Thursday afternoon, but an official who spoke on the condition of anonymity said, “The report clearly endorses Israel’s position regarding the legality of the naval blockade and its enforcement. We accept the report and its recommendations, and we hope that Turkey will do the same, opening a new possibility for reconciliation in spite of everything.”

Turkey’s representative to the panel, Suleyman Ozdem Sanberk, submitted a letter registering “disagreement” with several of the report’s conclusions, including its finding that the naval blockade is legal.

“Freedom and safety of navigation on the high seas,” he said, “is a universally accepted rule of international law. There can be no exception from this long-standing principle unless there is a universal convergence of views.”

The report’s finding on the legality of Israel’s naval blockade — first imposed in January 2009 — contradicted the conclusions of a fact-finding mission established last year by the U.N. Human Rights Council. But the report’s authors noted that the scope of their inquiry did not allow them to “make definitive findings either of fact or law. But it can give its view.”

Special correspondent Joel Greenberg in Jerusalem contributed to this report.