The mysterious "mass suicide" of 152 dolphins washed up on Iran's coast over the past month has alarmed environmentalists, with the blame pointed at regional fishing practices.

At the end of September, 79 Striped Dolphins were found washed up off the southern port of Jask in southern Iran, and last week another 73 dolphins were found dead in the same area.

Pictures of rows of dolphin corpses in the sand have been widely featured in Iranian newspapers, which said the dolphins had "committed suicide" - behaviour the animals have exhibited on occasion in the wild.

"The suicide of dolphins on Jask's coast continues," the Governmental Iran newspaper wrote on Saturday. "Locals tried to put the animals back in the water but they refused to return."

The scale of concern over the deaths of the highly intelligent mammals has prompted Iran's environmental protection authorities to show a dead dolphin corpse to the press to explain the "suicides".

Mohammad Baqer Nabavi, deputy head of Iran's environmental protection organisation in charge of marine biology, said the most likely explanation was that the dolphins drowned after becoming entangled in fishing nets rather than because of pollution.

"We did not spot pollution in the tissue of the dead dolphins a month ago," he told reporters.

"We are basing our hypothesis for the suicide on fishing - either nets left at the bottom of the Persian Gulf or the big fishing nets that ships spread to catch different kinds of fish," Mr Nabavi added.

"As you know, though, they are marine animals but they need to come up to surface and breathe."

A striped dolphin, normally found in temperate and tropical waters of the world's oceans, was frozen and shipped in from southern Iran for display and showed traces of bruising and cuts.

"We did not spot any kind of pollution in their digestive system that could have been caused from eating poisoned fish, and we also have not spotted any viruses or parasites," he added.

But he also emphasised that the mystery had still not been solved.

He said that a committee comprised of the oil ministry, Tehran University, veterinary and shipping organisations and even the Iranian naval forces had been set up to find the cause of the problem.

Mr Nabavi said that in the next two weeks there would be some preliminary results about the cause of the dolphins' deaths.

US nuclear-powered naval ships and other sophisticated marine craft have also been operating in the Gulf, using ultrasound tracking devices that sometimes hinder the eco-locations intrinsic in sea mammals such as dolphins.

The striped dolphin's colour is very conspicuous and makes it relatively easy to distinguish at sea. The underside is white or pink, and one or two dark blue bands run from the bottom of the eye to the flipper.

- AFP