Russia's antimonopoly watchdog has opened a case against gas company OAO Gazprom (GAZP.RS) after a complaint from oil producer OAO Rosneft (ROSN.RS) that it didn't allow access to its gas pipeline system, the agency said Wednesday.

Russia's antimonopoly watchdog has opened a case against gas company OAO Gazprom (GAZP.RS) after a complaint from oil producer OAO Rosneft (ROSN.RS) that it didn't allow access to its gas pipeline system, the agency said Wednesday.

Rosneft claims that between April and August, it was denied full access to Gazprom's pipeline system due to lower demand for gas in Russia, the Federal Antimonopoly Service, or FAS, said.

However, Rosneft says it has contracted all its gas production to domestic costumers.

The FAS Tuesday fined Rosneft 5.28 billion rubles ($182.4 million) for abusing its position on the wholesale fuel market in the first six months of 2009.