The water pollution came to light late last month after local surfers reported stinging eyes and said the water had changed color and developed an odor. Officials later confirmed the surfers had suffered mild burns to their corneas.

Then locals witnessed large numbers of dead sea creatures including seals, octopuses and sea urchins washed up onto a black-sanded beach popular with tourists.

The regional governor, Vladimir Solodov, said Monday that the sea off the remote Kamchatka peninsula may have been contaminated with toxic chemicals as Greenpeace warned of an "ecological disaster" for marine life.

Officials have said tests soon after found above-permitted levels of phenol and petroleum products.

Experts were investigating whether this was linked to "spills of some toxic substances," Solodov said in a statement.

He added that divers had confirmed the deaths of sea creatures and pollution appeared to be spread over a wide area.

Officials are scrambling to come up with the cause after President Vladimir Putin in June reacted angrily to the late reporting of an oil leak in Arctic Siberia that poured thousands of tons of diesel into land and waterways.

Ecology Minister Dmitry Kobylkin said in televised comments that Putin had ordered him to get to the bottom of the situation.

Read also: Siberian oil spill contaminates Arctic lake

Military sites 

The 38-year-old Kamchatka governor, dressed in a "I/We are the Pacific Ocean" T-shirt, vowed on Instagram to lead a "transparent" probe and sack any official who covered up the scale of the pollution.

He said there would be checks on Tuesday at two military testing sites, Radygino and Kozelsky, that could be responsible, citing a "yellow film" on a local river.

"Early tomorrow morning there will be inspections of two key test sites that are raising everyone's concerns," he said.

Some experts have suggested that highly toxic rocket fuel could have leaked into the sea.

The first test site, Radygino, is around 10 kilometers from the sea and was used for drills in August. 

Vladimir Burkanov, a biologist specializing in seals, in a comment published by Novaya Gazeta opposition newspaper suggested that old stores of rocket fuel kept in Radygino could have rusted and the fuel leaked into streams.

The other site, Kozelsky, has been used to bury toxic chemicals and pesticides, according to the governor's website.

Greenpeace said its team currently assessing the situation had seen patches of "yellowish foam" and murky water in several areas, with some pollution drifting towards a UNESCO-protected area of volcanoes.

The group said it saw dead animals in one area.

Ecology Minister Kobylkin said in televised comments that so far tests had only found slightly raised levels of iron and phosphates and suggested that the incident might not be manmade but caused by the stormy conditions and microorganisms altering the oxygen levels.

Environmental inspectors and experts from a fisheries and oceanography research center were set to continue tests.

Greenpeace said it had contacted state ecological monitors, the armed forces and the Prosecutor General's Office urging an immediate investigation. 

Prosecutors and investigators announced they would carry out checks into whether a crime had been committed but have not released any findings.

The emergencies ministry said it was using boats and drones to monitor the coastline but added that "no pollution is visible."

Governor Solodov said it was a problem that the region had no unified system of environmental monitoring.

The pristine peninsula is a popular destination for adventure tourism with its abundance of wildlife and live volcanoes.

The incident came as authorities urged tourists not to visit a live volcano on Kamchatka, warning eruption could be imminent.

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