United Nations, Sept 30 (NDTV.COM) Israel refused to give a UN-appointed investigation access to the officials who may have been responsible for the bombing of an observation post.

The attack killed four unarmed peacekeepers at the height of the Israel-Hezbollah conflict, the United Nations said.

Israel said the bombing of the post along the Israeli-Lebanese border was a mistake that occurred at the "operational level."

But the panel investigating the killings was not allowed to interview commanders at that level to determine what happened, UN spokesman Stephane Dujarric said in a statement.

The four observers were killed by an Israeli precision-guided bomb that destroyed the bunker where they took shelter after their observation post along the border came under heavy fire.

UN officials in New York and Lebanon had repeatedly warned Israel that the observation post, built 30 years before, was under attack.

Because of Israel's refusal, the inquiry was "unable to determine why the attacks on the UN position were not halted despite repeated demarches to the Israeli authorities from UN personnel, both in the field and at headquarters," Dujarric said.

The Board of Inquiry investigating the attack submitted a confidential report with its findings to the UN and to the four nations whose observers were killed, Austria, Canada, China and Finland.