DUBAI, UNITED ARAB EMIRATES, AUG. 22 -- The U.S. Navy shuttle service for reflagged Kuwaiti tankers moved into high gear today as a convoy of loaded vessels left for a trip south through the Persian Gulf only hours after three empty ships arrived safely in Kuwait harbor.

There was no official announcement when the supertanker Bridgeton and three other vessels departed, in keeping with U.S. policy of maintaining silence on ship movements. The Pentagon later confirmed that the ships were under way.

Helicopters from the assault ship USS Guadalcanal were believed to be sweeping for Iranian-laid mines ahead of the convoy, although it remained unclear whether Saudi Arabian mine sweepers also might be assisting.

It was the Bridgeton that struck a mine on its way to Kuwait in the first U.S.-protected convoy a month ago, leading to the decision to dispatch the mine-sweeping helicopters to the gulf.

As the test of wills between Iran and the United States continues in the gulf waters, Iraqi warplanes continued their renewed assault on Iranian economic targets.

The Iraqi military command said 40 warplanes struck Iran's unfinished $4 billion petrochemical complex in Bandar Khomeini, leaving it a "cloud of smoke."

The Iraqis have been hitting at Iranian industrial targets for the past week, although Iran claims that most victims of the attacks have been civilians. Iran said today that 25 people were killed in an attack on Bandar Khomeini earlier this week.