Russia's energy giant Rosneft risks breaking law unless it drops intentions to export petrol instead of selling it on the domestic market, the Federal Antimonopoly Service (FAS) said Wednesday.

"Export of petrol in the circumstances when there is unsatisfied domestic demand could result in groundless shortage of petrol," the FAS press service said in a statement.

Russia enacted the federal law "On Protection of Competition" in July 2006, which aims at preventing and restricting monopolistic activities and unfair competition.

FAS referred to Rosneft's plans to export more than 1.14 million tons of fuel between December 2014 and March 2015.

Rosneft explained its decision by anticipated decrease in demand for fuel during these months on the domestic market and claimed it so far has not sold any fuel abroad.

"We are going to monitor actions of the oil companies thoroughly, study reasons behind price increase and undertake measures if necessary," the FAS said at its website.

Earlier in December, President Vladimir Putin demanded to stop domestic fuel price hike in the circumstances when the world oil prices have been falling. The Russian oil companies have cut domestic prices by 0.40 rubles per liter following the warning.

Rosneft, Russia's largest oil producer and exporter, came under spotlight in October when its head Igor Sechin asked the government to subsidize the company from the National Welfare Fund to make up for losses incurred due to Western sanctions.

In December, FAS started investigating three other oil companies suspected in illegal price-fixing deals aiming at keeping petrol price tags high.

According to the organization, petrol wholesale prices have grown 35 percent in 2014. After FAS intervened, the prices went down by 7 percent from their highest level.