JERUSALEM, Aug 9 (Reuters) - Turkey ignored repeated warnings and appeals at the highest level to halt a Gaza aid flotilla, Prime Minister Benjamin Netanyahu told an Israeli inquiry on Monday into the fatal raid by his troops.

Netanyahu was the first witness to testify to the state-appointed inquiry into the lethal raid at sea on May 31, in which Israeli commandos killed nine Turkish pro-Palestinian activists after boarding their vessel from a helicopter.

The clash took place before dawn in international waters off Israel, after the flotilla ignored repeated Israeli warnings not to continue to Gaza. The enclave is ruled by the Hamas Islamist movement and is sealed off by an Israeli naval blockade.

The United Nations formed its own committee to investigate the Israeli raid, which will meet for the first time on Tuesday.

Beginning on May 14, my office held contacts with the highest levels of the Turkish government, Netanyahu said.

These contacts ... were intended to prevent a confrontation with the Marmara flotilla, and they continued until the eve of the flotilla's arrival off Gaza's shores, he said.

Despite our continuous diplomatic efforts, ultimately the Turkish government did not prevent the attempt by the Marmara to violate the naval blockade ... It appears that (Turkey) did not see in the prospect of a clash between Turkish activists and Israel something that clashed with its interests.

It was Netanyahu's most explicit public account of behind-the-scenes diplomacy that in the end failed to avert the confrontation.

After ending his testimony Netanyahu voiced his confidence that the commission would find Israel had acted properly.

I am convinced that when the committee will finish its work it will become clear beyond any doubt that the state of Israel acted according to international law, that the army acted according to international law, under the highest standards of the international community, that the soldiers defended themselves and accomplished their mission with extraordinary bravery under a real life threat. Netanyahu said.

Nine Turks were shot dead when Israeli commandos stormed the lead ship, Mavi Marmara. Israel says its commandos used live fire only after being attacked with clubs, knives and gunfire by activists who it says were clearly prepared for violence. Israel made video recordings of the fighting on deck.

The raid sparked a world outcry and almost ruptured Israel's relations with once-close Muslim ally Turkey.

It also pushed Israel to ease its Gaza blockade, which is aimed at preventing the territory's Hamas rulers from bolstering their weapons stockpile but also aggravates the privations of 1.5 million mostly aid-dependant Palestinians.

EXISTENTIAL THREAT

The Jerusalem-based inquiry is led by retired Supreme Court justice Jacob Turkel and includes two foreign observers. With a limited mandate, the panel's findings will likely have little effect on the stability of Netanyahu's government.

It is investigating the circumstances surrounding Israel's handling of the encounter with the six-vessel, Turkish-owned aid flotilla that was trying to bring aid to Gaza, and cast a spotlight on its blockade in a direct challenge.

A separate, internal probe by Israel's military, which included interviews with the commandos who stormed the ship, found intelligence and operational errors in planning but defended the soldiers' use of force.

Netanyahu said Israel could not have allowed the ships to breach its cordon, which it insists is necessary to keep weapons including long-range rockets out of the hands of Iranian-backed Hamas and other militant groups in the strip.

The state of Israel and the IDF (Israel Defence Forces) operated according to international law, he said. As prime minister I can't ignore Hamas as a threat to Israel's existence.

Netanyahu's spokesman Nir Hefetz told reporters that this inquiry was not an anti-Israel body unlike the U.N. Human Rights Commission under judge Richard Goldstone into Israel's devastating Gaza Strip offensive in January 2009.

Israel had refused to cooperate with the Goldstone probe.

Hefetz said the Turkel commission attests to the way in which the state of Israel, at the highest of international standards, is prepared to show its cards and say 'We have nothing to hide'.