A Russian unit of BP PLC on Friday denied Moscow's announcement it would be sued for oil leaks that have polluted two Siberian river basins, saying most of the damage is a result of inherited environmental problems, accumulated since 1962.

TNK-BP, Russia's third-largest oil company, pointed to its ongoing $500-million cleanup fund as evidence it is committed to greening up some of Russia's oldest oil fields.

The company's share price fell 5 percent on the Russian bourse after a government transcript was released quoting Yuri Trutnev, natural resources and ecology minister, as saying he ordered the environmental regulator Rosprirodnadzor to sue the company for damages and to force them to overhaul its pipeline system.

Energy Minister Sergey Shmatko accused the company of sacrificing pipeline maintenance in order to pay high dividends to investors. The company reported paying out $7.9 billion in dividends last year, Reuters reported.

The company's stock price fell 7.2 percent over a two day period, the furthest decline in seven months. An analyst for UralSib Financial Corp. said part of the reason for the decline was the market responding to a dividends report due out within a month, Bloomberg news agency reported.

The company said Friday it reduced spill and leak incidents by 21 percent and the amount of spillage by 60 percent in 2011 over the previous year.

Trutnev claims up to 500,000 metric tons of oil or related chemical products spill annually into the Ob and Yensin rivers and surrounding watersheds, and that TNK-BP is the biggest offender.

TNK-BP is a joint venture between BP and a consortium comprised of Access Industries, Alfa Group, and Renova. It has proven reserves of 8.2 billion barrels, and operates five refineries and 1,400 gas stations in Russia and Ukraine.