* Israeli diplomat quotes UNIFIL report on Aug. 3 clash

* Israel: UN says Lebanon guilty of "serious violation"

UNITED NATIONS, Aug 30 (Reuters) - A U.N. investigation into a deadly skirmish on the Israeli-Lebanese border has determined that Lebanon's army caused the clash in violation of a 2006 peace deal, an Israeli diplomat said on Monday.

U.N. peacekeepers in southern Lebanon, known as UNIFIL, said earlier this month that Israeli soldiers were operating inside Israel on Aug. 3 when a firefight broke out with Lebanese troops in the bloodiest border violence since a 2006 war.

After a unanimous vote by the 15-nation Security Council to extend UNIFIL's mandate for another 12 months, Israel's deputy ambassador to the United Nations, Haim Waxman, quoted what he said was a U.N. report on UNIFIL's investigation.

"The Lebanese Armed Forces opening fire, which triggered the exchange, constitutes a serious violation of resolution 1701 and a flagrant breach of the cessation of hostilities," Waxman quoted the UNIFIL report as saying.

"At the time of the initial Lebanese Armed Forces fire, the Israeli Defense Forces troops were positioned on the Israeli side, south of the Blue Line."

Security Council resolution 1701 halted hostilities in the Israeli-Hezbollah war in 2006 and banned all unauthorized weapons between the Litani River and the Blue Line, the U.N.-monitored border between Israel and Lebanon.

A senior Israeli officer, two Lebanese soldiers and a Lebanese journalist were killed in the Aug. 3 skirmish, which raised fears of wider conflict. [ID:nLDE6720V3]

U.N. officials had no immediate comment on the accuracy of Waxman's quotes from the UNIFIL investigation report.

The UNIFIL report was handed to Secretary-General Ban Ki-moon last week, with copies given to Israel and Lebanon, but has so far not been made public.

Russian Ambassador Vitaly Churkin, this month's Security Council president, said it would be distributed only to council members after a meeting on Thursday between the Lebanese and Israeli armies and UNIFIL. (Reporting by Louis Charbonneau; Editing by John O'Callaghan)