MOSCOW, Russia: Russian officials have said that some 2,500 Caspian seals have been found dead on the Caspian Sea coast in south of the country.

The cause of the mass deaths is unclear, but it was likely due to natural causes, said authorities in the Russian province of Dagestan.

Local officials reported 700 dead seals found along the coast, but this figure was later raised to some 2,500 by the Dagestan division of the Russian Ministry of Natural Resources and Environment.

In a statement, Zaur Gapizov, head of the Caspian Environmental Protection Center, said the seals died weeks ago, adding that there was no sign that they were killed or caught in fishing nets.

Federal Fisheries Agency and prosecutors inspected the coastline and collected data for laboratory research, but did not immediately discover any traces of pollutants.

Several previous incidents of mass seal deaths were attributed to natural causes. This year, Kazakhstan, which has a long Caspian coastline, has reported three such incidents.