"The overall number of dead seals as of Monday night reached 605, including 489 baby seals," the ministry said. "The coast is continuing to be monitored."
The dead seals have been found along the seashore between two major oil fields in western Kazakhstan. But officials in Kazakhstan cite weather conditions as a possible reason.
"Until February 20, most of the northeastern Caspian did not freeze..., and on February 21-22 the northern Caspian had a covering of thin ice, ...which melted by March 20, ... and it could have had a negative effect on the baby seals," the Ministry of Environmental Protection said earlier.
The ministry said an examination of the seals' bodies had not revealed the presence of any heavy metals or pesticides and "seawater tests carried out in the area did not reveal any oil products."
But the probe is continuing, and Environmental Protection Minister Nurlan Iskakov said earlier if oil companies were found guilty, they would be brought to justice.
"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.
Kalamkas and Karazhanbas are the largest oil fields in western Kazakhstan, where intensive production has been underway for more than 25 years.
In 2000, some 10,500 seals died of chronic intoxication in the area, according to findings made by Kazakh, Russian and Scottish experts. For several years the animals had been absorbing oil toxins and pesticides, which damaged their immune resistance, the experts said.