TEL AVIV, July 12 (Reuters) - An Israeli military inquiry released on Monday found intelligence and operational errors in a deadly raid on a Gaza-bound aid flotilla but defended the use of force behind the killings of nine Turkish activists.

The report was the first of two separate investigations including a judicial-headed panel named by Prime Minister Benjamin Netanyahu's government into the May 31 raid that strained Israel's relations with Muslim ally Turkey and brought a world outcry that forced it to ease its land blockade on Gaza.

Giora Eiland, a reservist general who headed the army's panel, said, summarising the findings of a 150-page document, which is classified, supported the use of force and the need for commandos to board one of the vessels so as to intercept it.

But on the other hand there were mistakes that were made in decisions, including some taken at relatively high levels, which meant that the result was not as had been initially anticipated, Eiland told reporters at the army's headquarters.

We found there were professional mistakes regarding intelligence and the decision-making process, he added, and also cited what he called operational mistakes.

A senior security official said a plan devised before the incident, was reasonable but may have made a wrong assumption about expecting a dozen or so soldiers to easily subdue a shipload of activists bent on attacking them.

The team of eight investigators concluded that not all possible intelligence gathering methods were fully implemented and various intelligence units failed to coordinate, an army statement said, adding that the anticipated level of violence used against the forces was underestimated.

Some of the commandos, the Israeli military has said, were armed with paintball guns -- but also carried pistols -- in anticipation of only light resistance.

Eiland, who briefed reporters at the military's headquarters in Tel Aviv, said better intelligence on the the activists' plan to attack Israeli commandos may have helped prevent bloodshed.

'NO FAILURE OR NEGLIGENCE'

The military's chief of staff, Lieutenant-General Gabi Ashkenazy said in a statement that no failure or negligence was found but that there were mistakes which must be corrected.

There was evidence that activists on the Turkish-flagged Mavi Marmara opened fire on Israeli commandos, at least in one instance using a weapon they had on board, a senior Israeli security official said.

Activists took three soldiers hostage, an incident that prompted one of the troops to open fire as he boarded the vessel, in an attempt to rescue them and to help extricate wounded forces, the official added.

The official who spoke on condition of anonymity said there was a high probability at least one activist had fired the first shot and ballistics tests showed a bullet from a soldier's wound was not fired from an Israeli-issue weapon.

Eiland said the army also had evidence that there was at least one weapon on this ship before we arrived and four incidents in which activists opened fire at the troops.

Turkish organisers of the flotilla say activists seized guns from Israeli commandos but threw them overboard.

Eiland said soldiers fired live ammunition only when they were under real danger to their lives and that overall the commandos acted in a very professional way in response to being attacked by metal rods and knives.

Israel says its naval blockade of Gaza is intended to prevent weapons from reaching its Hamas rulers, but has eased a land embargo of the territory since the flotilla incident.

The civilian panel named by Israel is headed by a former Supreme Court justice, Jacob Turkey, and includes two international observers, but its mandate is seen as too narrow to pose any political threat to Netanyahu. (Additional reporting by Joseph Nasr and Ori Lewis in Jerusalem)