Israel exhausted all other options before carrying out its deadly raid on a Turkish aid flotilla enroute to the blockaded Gaza Strip, Defence Minister Ehud Barak told a government-appointed inquiry on Tuesday.

Barak also said he was told by Israel's military chief that the operation "won't be simple, but we can get it done".

Nine Turks were shot dead when Israeli commandos stormed the lead ship on May 31. 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.

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

It also pushed Israel to ease restrictions of its Gaza blockade, which is aimed at preventing the territory's rulers Hamas from increasing their arms arsenal but also aggravates the privations of 1.5 million mostly aid-dependent Palestinians.

Testifying before the panel a day after Prime Minister Benjamin Netanyahu, Barak said the decision to stop the 6-ship convoy came after "diplomatic efforts didn't bear fruit", and after "weighing all the possibilities and taking into account the different risks".

Barak, himself a former commando and top general, said the military's intelligence had warned of a potential "collision and friction" during the raid, but not at the level encountered.

"There is never perfect intelligence before a mission," he said. Israel's military chief, Lieutenant-General Gabi Ashkenazi, will give testimony on Wednesday.

The United Nations has formed its own committee to look into the raid. It is due to meet for the first time later on Tuesday.