Two American fighter jets dropped four unarmed bombs into Australia's Great Barrier Reef Marine Park last week when a training exercise went wrong, the U.S. Navy said Saturday, angering environmentalists and politicians.

The two AV-8B Harrier jets launched from aircraft carrier USS Bonhomme Richard each jettisoned an inert practice bomb and an unarmed laser-guided explosive bomb into the World Heritage-listed marine park off the coast of Queensland last Tuesday, the 7th Fleet said in a statement Saturday reported by the Associated Press. The four bombs, weighing a total 1.8 metric tons (4,000 pounds), were dropped into more than 50 meters (164 feet) of water away from coral to minimize possible damage to the reef, the statement said. None exploded.

The U.S. Navy has promised to retrieve the bombs, the Australian newspaper the Age reports. Spokesman Cmdr. William Marks said each bomb was jettisoned in a ''safe, unarmed state and did not explode.'' The Australian Defence Force said the bombs posed ''minimal risk.''

The jets from the 31st Marine Expeditionary Unit had intended to drop the ordnance on the Townshend Island bombing range, but aborted the mission when controllers reported the area wasn't clear of hazards. The pilots conducted the emergency jettison because they were low on fuel and couldn't land with their bomb load, the Navy said.

The emergency happened on the second day of the biennial joint training exercise Talisman Saber, which brings together 28,000 U.S. and Australian military personnel over three weeks. The U.S. Navy and Marine Corps were working with Australian authorities to investigate the incident, the Navy said. A 7th Fleet spokesman didn't immediately respond on Sunday when asked by email whether the dumping posed any environmental risk.

Australian Sen. Larissa Waters, the influential Greens party's spokeswoman on the Great Barrier Reef, described the dumping of bombs in such an environmentally sensitive area as "outrageous" and said it shouldn't be allowed. "Have we gone completely mad?" she told Australian Broadcasting Corp. "Is this how we look after our World Heritage area now? Letting a foreign power drop bombs on it?"