Two US fighter jets have dropped four unarmed bombs in Australia's World Heritage-listed Great Barrier Reef marine park after a training exercise went wrong.

The AV-8B Harrier jets took off from the aircraft carrier USS Bonhomme Richard and each released an inert bomb and an unarmed explosive bomb off the coast of Queensland, the US 7th Fleet said in a statement on Saturday.

The four bombs, weighing a total 1.8 metric tons (4,000 pounds), were dropped in more than 50 meters (164 feet) of water away from coral that was supposed to have minimized possible damage to the reef, the statement said. Each Harrier jet dropped two 227-kilo bombs: one BDU 45 and one High Explosive GBU 12. None of the bombs exploded as the BDU 45s are inert and the GBU 12s were unarmed when released.

The training mission went gone wrong as the jets from the 31st Marine Expeditionary Unit were originally told to drop the bombs at the Townshend Island bombing range. That plan was aborted after the controllers said the area was not clear of hazards.

The pilots then went ahead with an emergency jettison as they were not allowed to land with bombs on board and both were low on fuel, the navy said.

The US Navy and Australian authorities are now investigating the incident.



The US Navy is planning to recover the bombs that are lying about 100 kilometres offshore and about 16 nautical miles south of Bell Cay in the Great Barrier Reef Marine Park. The US say that the chance of the bombs exploding was extremely remote.



''Due to low fuel and the inability to land with the amount of ordnance they were carrying, the on-scene commander determined it was necessary to designate an emergency jettison area for the ordnance,'' US Navy spokesman Commander William Marks said.



He said each bomb was jettisoned in a ''safe, unarmed state and did not explode''.

The Australian Defense Force said the bombs posed ''minimal risk or threat to the public, the marine environment or civilian shipping passing the reef area'', according to AP.



''The incident is being investigated by the US and findings will be provided to the Great Barrier Reef Marine Park Authority so that the way ahead can be mutually agreed,'' a spokesman said.

Senator for Australian Greens Party Larissa Waters has called the dumping of bombs on the World’s Heritage-listed site "outrageous''.



"We're letting the US military drop bombs on the World Heritage Great Barrier Reef. I mean, have we gone completely mad? Is this how we look after our World Heritage areas now? Letting a foreign power drop bombs on it?"



The failed training mission happened on the second day of the biennial joint training exercise Talisman Saber that brings together 28,000 US and Australian military personnel over three weeks.

Environmentalists and anti-war activists Graeme Dunstan, who is against the joint exercise, said that the incident proves the US cannot be trusted to protect the environment.

“How can they protect the environment and bomb the reef at the same time? Get real,” Dunstan told AP.

The Great Barrier Reef is a UNESCO World Heritage Site and is the world’s largest coral reef system, made up of over 2,900 individual reefs and 900 islands, stretching for more than 2,600 kilometers (1,600 miles) along the Australian northeast coast.