About 2,500 seals have been found dead on the Caspian Sea coast in southern Russia, officials said Sunday.

The authorities in the Russian province of Dagestan said that it's still unclear what caused the animals' deaths, but they likely died of natural reasons.

Regional officials initially said Saturday that 700 dead seals were found on the coast, but on Sunday Zaur Gapizov, head of the Caspian Environmental Protection Center, said according to the state RIA Novosti news agency that after a broader inspection of the coast the number of dead animals was 2,500.

Gapizov said the seals likely died a couple of weeks ago. He added that there was no sign that they were killed by poachers.

Experts of the Federal Fisheries Agency and prosecutors inspected the coastline and collected data for laboratory research, which didn't immediately spot any pollutants.

Several previous incidents of mass deaths of seals were attributed to natural causes.

The data about the number of seals in the Caspian varies widely. The fisheries agency has said the overall number of Caspian seals is 270,000-300,000, while Gapizov's center put the number at 70,000.