The Australian Defence Force Investigation Service is investigating why a sailor aboard HMAS Toowoomba died from a gunshot wound in his cabin while the frigate was docked at Mumbai port in India.

The 28-year-old sailor, who is not being named, was found dead inside his cabin, the Department of Defence said on Monday, according to Sky News. His family had been notified.

The Chief of Navy and all members of the Navy family are saddened by this loss and offer their condolences to the family,'' Defence said in a statement, according to Perth Now.

Officials from the Australian embassy in Mumbai will join the investigation.

The Toowoomba was on a routine visit to Mumbai while en route to Fleet Base West in Garden Island south of Perth. It just finished a six-month duty in the Persian Gulf in support of the war in Afghanistan. Its 190 sailors under Commander Andrew Quinn provided medical and engineering assistance to numerous vessels during the mission called Operation Slipper.

The HMAS Parramatta took over Toowoomba's place on Oct. 18 to continue Operation Slipper. Parramatta will be in the Persian Gulf until Nov. 7, when the HMAS Stirling will take over its role.

Mystery surrounds the death of a sailor aboard the HMAS Toowoomba while docked at Mumbai port.