Russian President Vladimir Putin said on Thursday he signed a decree that mandates “unfriendly” foreign buyers must pay in rubles for Russian gas starting on April 1. If payments aren’t made in Russia’s currency, contracts will be halted, the Russian president said. A number of European countries rely heavily on Russian gas and oil, meaning that a halt in gas exports could plunge those countries into a significant energy crisis. “In order to purchase Russian natural gas, they must open ruble accounts in Russian banks. It is from these accounts that payments will be made for gas delivered starting from tomorrow,” Putin said in televised remarks. “If such payments are not made, we will consider this a default on the part of buyers, with all the ensuing consequences. Nobody sells us anything for free, and we are not going to do charity either … that is, existing contracts will be …