NEW YORK (AP) -- Israel's UN ambassador on Thursday ruled out major UN involvement in any potential international force in Lebanon, saying more professional and better-trained troops were needed for such a volatile situation.

Dan Gillerman also said Israel would not allow the United Nations to join in an investigation of an Israeli airstrike that demolished a post belonging to the current UN peacekeeping mission in Lebanon. Four UN observers were killed in the Tuesday strike.

"Israel has never agreed to a joint investigation, and I don't think that if anything happened in this country, or in Britain or in Italy or in France, the government of that country would agree to a joint investigation," Gillerman said.

Gillerman, who spoke at an event hosted by The Israel Project advocacy group and later inside the United Nations, gave a heated defense of Israel's two-week campaign against Hezbollah militants.

He said some diplomats from the Middle East had told him that Israel was doing the right thing in going after Hezbollah.

His refusal to conduct a joint investigation will be a slap to UN officials, who have specifically sought to partner with Israel to investigate the bombing.

Gillerman was highly critical of the current UN peacekeeping force, deployed in a buffer Zone between Israel and Lebanon since 1978, saying its facilities had sometimes been used for cover by Hezbollah militants and that it had not done its job.

"It has never been able to prevent any shelling of Israel, any terrorist attack, any kidnappings," he said. "They either didn't see or didn't know or didn't want to see, but they have been hopeless."

Gillerman even mocked the name of the force — the UN Interim Force in Lebanon.

"Interim in UN jargon is 28 years," he said.

The flaws with the UN force make it imperative that any UN force come from somewhere else, though it could have a mandate from the United Nations, he said.

"So obviously it cannot be a United Nations force," Gillerman said. "It will have to be an international force, a professional one, with soldiers from countries who have the training and capabilities to be effective."

Any such force must have two main objectives. It must disarm Hezbollah completely and make sure that the group has lost all its capacity as a terror organization; and it should monitor the border between Syria and Lebanon "to make sure that no additional shipments of arms, rockets, illegal weapons, enter Lebanon," he said. Despite his refusal for a UN force, he said Israel was not "excluding anybody," and that "the makeup, the composition and the countries which would supply the soldiers to that force still has to be decided."

Gillerman apologized for the strike that killed the four UN observers, but said the conflict was a war and that accidents happen.

"This is a war which is going on," he told reporters. "War is an ugly thing and during war, mistakes and tragedies do happen."

Gillerman said Israel would welcome any information from the UN as it conducts its investigation, and will consider any UN requests for information.