Hundreds of dead seals have washed up on Kazakhstan's Caspian Sea shoreline in the past several days, bringing the total number of the animals found dead along the shoreline in recent weeks to 832, the Emergencies Agency said Wednesday.

Environmental officials in the Central Asian nation were trying to determine what killed seals — most of them young — the agency said in a statement. Preliminary tests showed some of the animals were infected with the distemper virus, authorities said.

Several dozen dead seals were found by oil workers on the Caspian shore in western Kazakhstan's Mangistau region about a month ago. By mid-April, the number had risen above 500.

A series of viral epidemics have killed thousands of Caspian seals since the late 1990s.

Environmentalists have also been concerned about the effect on wildlife of increasing exploration of the inland sea's extensive oil reserves.

Last year, 350 seals and thousands of sturgeon died as a result of a heavy metal leak from an oil field.