DHAHRAN, SAUDI ARABIA, JAN. 2 -- Six mines of unknown origin were found floating in the Persian Gulf last month, a U.S. Navy spokesman said here tonight.

Five of the contact mines, which posed a threat to the allied warships in the gulf as well as offshore oil facilities, were destroyed by Saudi or U.S. explosives disposal teams, Lt. Col. Greg Pepin said. The sixth will be destroyed "shortly," he said.

The disclosure followed a "navigation warning" cautioning shippers about floating mines in the gulf. It was issued by Lloyd's of London, the British maritime insurance underwriters, on Dec. 30. It urged vessels in the gulf to "exercise extreme caution" in the vicinity of the Saudi offshore oil field of Al-Zuluth "due to the probable presence of mines."

Lloyd's said its advisory stemmed from the discovery of a floating mine on Dec. 30 near Al-Zuluth, which is off the coast of Saudi Arabia near its border with Iraqi-occupied Kuwait.

Meanwhile, unconfirmed reports have circulated that an offshore oil facility in Saudi Arabia's Safaniyah oil field was damaged Sunday or Monday by a floating mine. The reports, which came from two separate sources, left unclear the extent of damage and whether the damaged facility was a pumping station or a loading platform. The Safaniyah field is a few miles west of the Al-Zuluth field.

A spokesman at the U.S. military press office in Riyadh, asked about the report, referred a reporter to Saudi Aramco, the state-owned oil company that operates both oil fields. An Aramco spokesman declined to comment on the report, saying all press inquiries must be directed to Saudi Arabia's Ministry of Petroleum. Ministry officials could not be reached.

Officials at Lloyd's said today they had received no information about any mine damage to an oil installation.

Pepin said all the mines detected and disposed of by the allied forces were "floating contact mines" that "apparently {had} broken loose from their bottom moorings."

Another source said the mines were all detected off the coast of Saudi Arabia just south of Kuwait between Dec. 22 and 30 and that it was unusual to find so many mines within such a short period.

Pepin said military officials are trying to determine where the mines came from. He said that "overall, very few mines have been detected in the {Persian} Gulf."