From March 31 through April 8 266 dead seals were washed up along the sea shore from the Kalamkas oil field to the Karazhanbas field in western Kazakhstan, with more than half of them being baby seals.
Kazakh Environmental Protection Minister Nurlan Iskakov said if oil companies were found guilty, they would be brought to justice.
Iskakov said, "[They could face] fines, penalties and the suspension of oil production until the reasons [for the large number of deaths] have been established."
He said a special commission was investigating the causes of animals' death, which could take another two weeks.
"There are quite a few dangers in the area: blowing wells, tectonic fractures with the risks of gas discharges and exploration drilling," the minister said.
Iskakov said he had already issued instructions to "prohibit the disposal of waste from drilling on Caspian offshore areas."
Kalamkas and Karazhanbas are the largest oil deposits in western Kazakhstan, where intensive production has been underway for more than 25 years.
In 2000, some 10,500 seals died allegedly of chronic intoxication on the Caspian Sea shore in western Kazakhstan. For several years the animals had been absorbing oil toxins and pesticides, which damaged their immune resistance.
The official conclusion at that time was based on research by the Kazakh State Research Antiplaque Institute, the Caspian Fisheries Research Institute in Astrakhan in southern Russia and one of the world's leading experts in seals, Professor Callan Duck from the University of St. Andrews in Scotland.