Lima - Nearly 900 dolphins that washed up along Peru’s northern coast since the start of the year died of natural causes, said Peru’s production minister on Tuesday.

“We have reached the conclusion that the deaths were from natural causes,” said Gladys Trevino.

She said a study by the government-run Institute of Peru's Ocean (IMARPE) had ruled out other explanations such as offshore oil exploration or viral or bacterial infections.

Environmental groups, however, remained unconvinced and said they were certain the die-off was linked to offshore oil exploration in the area.