Russian President Vladimir Putin has ordered an investigation into the cause of an Arctic oil spill last week.

A fuel tank at a power plant near the city of Norilsk in Siberia collapsed on May 29, leaking 20,000 tonnes of diesel oil into a river within the Arctic Circle, reports Efe news.

On Friday, Putin has demanded that Russian authorities bring the situation under control and investigate the cause of the incident after previously declaring a state of emergency over the disaster.

“I ask all the agencies that should be directly involved in this work, certainly the Ministry of Emergencies, to establish full special control over the situation,” he was quoted by Russian news agency TASS.

“Definitely, causes should be identified and damages should be assessed thoroughly and uncompromisingly, objectively.”

The President also ordered Russia’s environmental watchdog to check all storage facilities for oil products in the country.

“I ask Russia’s Federal Supervision Service for Natural Resources Management to analyze thoroughly the condition of similar facilities across the entire country and organize checks, if necessary, including involving emergencies ministry specialists and law enforcers,” he added.

Emergency Minister Yevgeny Zinichev flew over the affected area on Thursday along with a commission created to respond to the ecological disaster.

It was the first incident of such a magnitude in the Arctic and is comparable to the Exxon Valdez tanker spill three decades ago off the coast of Alaska, according to Greenpeace.

Russian Deputy Minister of Natural Resources and Ecology Elena Panova said at a press conference on Thursday that the recovery of the environment in the area could take at least 10 years.

The cleanup has been complicated by the conditions in the area, she added.

Around 6,000 tons of diesel spilled onto the land and another 15,000 tonness went to rivers, according to state watchdog for natural resources Rosprirodnadzor.

A deployment of 70 rescuers from various Russian regions has been dispatched to the scene, in addition to special equipment from the Russian oil companies, including pumps, machines to collect oil, excavators and floating containment barriers.

Drones and helicopters have been sent to monitor the disaster area from the air.

Nornikel, the company responsible for the spill, has also been involved in the cleanup operation and has said the bulk of the fuel can be collected from local rivers within 14 days if conditions are favorable.

A criminal case has been opened into the incident for negligence, land damage, violation of environmental protection standards at work and water pollution.