The Russian government has decided to extend the gasoline export duty increase introduced in sping to protect the domestic fuel market and overcome gasoline shortages, a government resolution published in the newspaper Rossiiskaya Gazeta said on Friday. The government boosted the gasoline export tariff to a nearly prohibitive 44 percent from May 1 to fight local shortages which started in April in some regions.  Russian oil companies prefer to sell gasoline abroad where prices are higher than in Russia, where the state has capped prices. The  Federal Antimonopoly Service, the government\'s competition watchdog, has accused large oil firms of operating a cartel. The government believes that the introduction of an exchange trade in oil products will help regulate the market and has ordered companies to sell 15 percent of their products via exchanges. Gasoline price rises were reported across the country at between 2 and 20 percent several weeks ago. A large number independent filling stations not belonging to major oil companies ceased trading because of a lack of fuel in the Altai region in southern Siberia. The deficit later spread further, to the Siberian cities of Tomsk, Irkutsk and Novosibirsk, where filling stations are either closed or sell limited amounts of gasoline. Shortages were also felt in Murmansk in the northwest of Russia.