"An oil leak from the Katanglineftegaz pipeline formed a slick of some 5,000 square meters (54,000 square feet) on the ice of Lake Bedinga," the ministry said in a statement.

"Some of the oil sank under the ice and has polluted the waters of the lake," the statement said, adding that work to pump out the sunken oil was nearly complete.

An investigation has been opened into the damage caused to the pipeline, which belongs to the Russian oil giant Rosneft.

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