The crocodiles, called gharials, have been found dead in the Chambal river sanctuary in central India over the past month.

Gharials have a long, narrow snout and are native to the Indian subcontinent. Only about 2,000 of the critically endangered reptiles are believed to exist in the wild.

Forest officials have ruled out poaching, but are yet to find out the cause of death.

"It seems they were suffering from some unknown disease," said G. Sudhakhar, district forest officer at the Chambal Sanctuary.

The fish-eating reptiles could also have died of food contamination, senior forest official S.P Sharma said in Bhopal, capital of central Madhya Pradesh state, where some of the crocodiles were found.