By Polina Devitt, Rajendra Jadhav and Roberto Samora MOSCOW, Dec 21 (Reuters) - Global potash prices are set for an extended rally after the United States imposed sanctions on major supplier Belarus Potash Company (BPC), piling more pressure on farmers and consumers already facing rocketing costs and a global economy navigating rising food inflation. BPC typically agrees annual supply contracts with India with the most recent deal signed in January. However, public pressure on state firms to comply with the U.S. sanctions is rising in Vilnius, one of Europe's most vocal critics of human rights abuses in Belarus.