About half of the spillage flowed into a tributary of the Klyazma River near the town of Korolyov, affecting hundreds of wild birds. Rescuers are continuing to collect fuel from the spill site.
"Investigators found that depressurization of a metal container took place in a workshop at the Energia rocket and space corporation," the prosecutor's Moscow Region office said on its website, calling the accident an environmental disaster.
Prosecutors also pledged to determine the degree of culpability of the enterprise's managers, and authorities monitoring the technical condition of containers and other storage equipment.
Environmental groups have repeatedly criticized Russian authorities for leniency in dealing with environmental crimes.
Under Russian law the mishandling of environmentally hazardous substances envisions a fine of 100,000-300,000 rubles ($4,000-$16,000) or up to five years in prison.
A total of 411.5 metric tons of fuel oil from the latest spillage have been collected since the start of the cleanup effort, including over 50 metric tons in the past 24 hours, the emergencies ministry said on Thursday.
Authorities have given assurances that fuel will not pollute the Klyazma.
