The preliminary injunction issued on Thursday requires the Navy to create a 12-nautical-mile no-sonar zone along the coast and have trained lookouts watch for marine mammals before and during exercises.

Sonar should be shut down when mammals are spotted within 2,010 metres.

The Natural Resources Defence Council had sued to force the Navy to lessen the harm of its sonar exercises.

In November, a federal appeals court said the sonar problem needed to be fixed and sent the matter to a trial judge in Los Angeles to hammer out the details.

Critics contend sonar has harmful effects on whales, possibly by damaging their hearing, and other marine mammals worldwide. The council's lawsuit alleges the Navy's sonar causes whales and other mammals to beach themselves.

The Navy has said the exercises are vital for training and claims it already minimises the risk to marine life. -- AP