The European Union warned Russian President Vladimir Putin Thursday not to risk his country’s role as a secure supplier of gas to the bloc and said Brussels was willing to start three-way talks quickly with Moscow and Kiev to resolve any concerns. In a letter to Mr. Putin, José Manuel Barroso, the president of the EU’s executive, said the “contractual reliability of the Russian Federation as a supplier of gas is at stake in this matter.” The EU meets around a quarter of its gas needs from Russian imports, around half of which reach the bloc through Ukraine. In 2009, some EU consumers were left without energy after pipelines between Russia and Ukraine were shut. Last week, Mr. Putin sent a letter to 18 European leaders, in which he said Russia could force Ukraine to make prepayments for its gas supplies because of […]