UNITED NATIONS — Israel apologized but refused to let UN investigators contact Israeli commanders responsible for the mistaken bombing that killed four unarmed peacekeepers in Lebanon during the Israel-Hezbollah fighting there in July, a UN official said Friday.

Without such access, the UN said it could not verify Israel's explanation that an "operational error'' resulted in the air strike that killed the four peacekeepers -- from Canada, Austria, China and Finland.

The United Nations is standing by Secretary General Kofi Annan's original assertion that the bombing was apparently "deliberate,'' the senior UN official told reporters.

"We do not have a satisfactory answer as to the question of why repeated attempts at all levels to intervene and halt the firings on, or close to, Patrol Base Khiam failed,'' said the official, speaking on condition of anonymity.

The UN observation post and patrol base near the southern Lebanese town of Khiam came under Israeli fire July 25, including four artillery shells that made direct hits. The United Nations repeatedly asked the Israeli Defence Forces to halt the bombardment, without success.

After the headquarters of the United Nations Interim Force in Lebanon, or UNIFIL, lost contact with the base, two armoured personnel carriers were sent to the site. They found the base destroyed and the four peacekeepers dead.

They were Maj. Paeta Hess-von Kruedener of Kingston, Ont., Maj. Hans Peter Lang of Austria, Maj. Zhaoyu Du of China, and Lt. Jarno Tapio Makinen of Finland.

"The Israelis have fully acknowledged their responsibility for this attack that they attribute to operational error,'' the UN official said. "They have apologized. We accept their apology.''

According to the UN report, the observation post was hit by a 500-kilogram precision-guided bomb that destroyed the structure.

"It was precisely guided, technically, through technical means, to this location on the ground,'' the official emphasized. "It was meant to hit this location.''

Israel blames the mistaken bombing on faulty military maps and explained that Israeli forces had meant to hit a Hezbollah rocket-launching site nearby.

The United Nations says it could not verify or refute Israel's claims because UN investigators were refused access to field commanders or the pilot who dropped the bomb.

"Our dialogues were restricted to senior Israel Foreign Affairs and IDF persons and government officials. So we do not have an ability to verify how the operational error occurred,'' the UN official said.

As for the claim that there was Hezbollah activity nearby, the UN official said: "On that day what the board did find was that there was no evidence of Hezbollah firing in or near Patrol Base Khiam within that period of time under examination.''

The UN says it has provided the Israelis with precise co-ordinates of all UNIFIL positions, including the Khiam base, on several occasions.

The UN report was presented to the four governments whose soldiers were killed but not released to the public. Reporters were briefed on its contents by the UN official.

Col. Michael Hanrahan of the Department of National Defence said Canada is pleased that the full report has been turned over and "it will be very helpful'' toward Canada's own investigation.

Lt. Carolle Brown, a spokesperson for DND, said Canada would not comment on the UN's report until its own investigation was concluded.

Two weeks ago, Israel briefed the governments of Canada, China, Austria and Finland on the findings of the Israeli inquiry but did not release the full contents of its report to them.