Water pollution in Russia’s Kamchatka peninsula that caused sea creatures to wash up dead on beaches has prompted fears that rocket fuel stored in the region’s military testing grounds may have leaked.

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

Then locals reported seeing large numbers of dead marine species including seals, octopuses and sea urchins washed up on a black-sand beach popular with tourists.

The regional governor, Vladimir Solodov, said on Monday the sea off the remote Kamchatka peninsula may have been contaminated with toxic chemicals. Greenpeace, which has been assessing the area, warned of an “ecological disaster”.

Officials said tests showed above-permitted levels of phenol and petroleum products. Experts were investigating whether this was linked to spills of toxic substances, Solodov said.

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 find 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.

The ecology minister, Dmitry Kobylkin, said in televised comments that Putin had ordered him to establish the cause of the situation.

The Kamchatka governor, dressed in a “I/We are the Pacific Ocean” T-shirt, vowed on Instagram to lead a “transparent” investigation 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 highly toxic rocket fuel could have leaked into the sea. The first test site, Radygino, is about six miles (10km) from the sea and was used for drills in August.

Vladimir Burkanov, a biologist specialising in seals, in a comment published by the Novaya Gazeta opposition newspaper, suggested 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 had seen patches of yellowish foam and murky water in several locations, with some pollution drifting towards a Unesco-protected area of volcanoes. The group said it saw dead animals in one area.

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

Environmental inspectors and experts from a fisheries and oceanography research centre were continuing 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 no pollution was visible. 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 because of an abundance of wildlife and live volcanoes. The incident came as authorities urged tourists not to visit a live volcano on Kamchatka owing to fears of an imminent eruption.