(Adds source of oil spill, number of ducks killed)

MOSCOW, Jan 11 (Reuters) - Russian volunteers on Friday scooped dead ducks out of a river near Moscow polluted by an oil spill from a fuel depot at a factory, a leak which is threatening to spread and contaminate drinking water.

The oil leaked into the River Dulov on Sunday from a factory which is involved with developing space rocket technology, conservation group WWF said.

WWF said the spill measured around 500 tonnes and had killed around 100 ducks. It accused the authorities of playing down its size and being slow to respond.

"Local authorities in the first days after the accident did not take any action and lost a lot of time," WWF representative Alexei Knizhnikov said in a statement.

"Once again, we are certain that there is no willingness to put into action the appropriate, civilised rescue operation with oil spills which involve caring about animals in distress."

WWF said that ice is preventing the oil from seeping into the River Klyazma, the main water source for thousands of people living to the east of Moscow, into which the River Dulov flows.

In November, a storm smashed an oil tanker near Russia's Black Sea coast, spilling hundreds of tonnes of oil which coated thousands of birds in thick sludge.

A senior official from Moscow's emergencies department said the spill had been controlled.

"This is not an ecological disaster," said Oleg Lomakin, first deputy chief for Moscow emergency department. (Writing by James Kilner; editing by Keith Weir)

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