ALMATY, Kazakhstan - Nearly 250 dead seals have washed up on the shores of the Caspian Sea in Kazakhstan in the past week, emergency officials said Saturday.

Authorities were conducting tests to determined what killed the 247 seals found by oil workers inspecting the shore in western Mangistau region, the Emergencies Agency said.

Environmentalists have been concerned about increasing exploration of the Caspian Sea's extensive oil reserves.

Last year, 350 seals and thousands of sturgeon died in a northern part of the Caspian region as a result of a heavy metal leak from the Kashagan oil field.

Also, several epidemics of a viral disease have killed thousands of Caspian seals since the late 1990s.