Conservationists have asked prosecutors to investigate whether the Kremlin's envoy to the State Duma was participating in an illegal hunt of endangered animals when the helicopter he was riding in crashed last week in the Altai region, killing him and six others.

Photographic evidence suggests that the late Duma envoy, Alexander Kosopkin, may have been part of a hunting expedition targeting an endangered species of wild sheep from the air when the group's Mi-171 helicopter went down last Friday, the World Wide Fund for Nature, or WWF, said Wednesday.

The organization asked the Prosecutor General's Office on Tuesday to open a criminal investigation into the expedition's purported poaching of the argali, a rare breed of wild sheep listed in Russia's Red Book of endangered species, said Igor Chestin, director of WWF's Russian operations.

Greenpeace said it would join the WWF in pushing for an investigation.

Calls to the Prosecutor General's Office for comment went unanswered Wednesday, while an Investigative Committee spokeswoman said it had not opened up a probe.

Under the Criminal Code, a state official using his position to hunt illegally can be punished by up to three years in prison and fined up to 300,000 rubles ($9,500).

Photographs of the crash site taken by Altai journalists and published on the web site Altapress.ru show dead argali sheep on the ground near the wreckage of the helicopter.

"Cases of top officials engaging in illegal hunting in Russia happen quite often, but most of them can't be proved," Chestin said.

The Argali is a globally endangered species, of which there are just 200 specimens remaining on the territory of the Altai region and Mongolia, Chestin said.

Natural Resources and Environment Ministry spokeswoman Anna Medoyan said she was unaware of any allegations of illegal hunting of the endangered species.

The helicopter took off with eight passengers and three crew members from the Altai regional town of Biisk at 8:30 a.m. Friday and failed to contact dispatchers as planned at 2 p.m. when it was scheduled to land in the village of Kosh-Agach, 500 kilometers away, according to the Altai government.

The wreckage of the white-and-blue helicopter was located at 3:35 p.m. Sunday in snowy mountainous terrain. Four injured survivors were rushed to the hospital.

Killed in the crash along with Kosopkin was Sergei Livishin, a senior member of the presidential administration; Viktor Kaymin, a senior Altai environmental official; Gorno-Altaisk aircraft division head Vladimir Podoprigora; and Vasily Vyalkov, the frontman of the regional music band Armanka.

Survivors included Nikolai Kopranov, an adviser to the Duma's Economic Policy Committee, and Boris Belinsky, a Moscow entrepreneur.