Russian officials have brought charges against four companies in the Far East which have been keeping some 100 whales in small, crowded pools that environmentalists have dubbed a "whale prison."

The Border Guards Department said Thursday that it suspects that the four companies captured the whales illegally. It also confirmed the environmentalists' claims that the belugas and orcas are kept in cramped conditions in a marine containment facility near Vladivostok and that they need to be released back. The border guards did not specify, however, when it will happen.

Activists raised the alarm late last year when the whales were captured off the Pacific Coast. Russian law only allows for the capture of whales for "scientific" purposes. But activists believe the whales have been captured for sale to foreign circuses.