By George Georgiopoulos and Matthias Williams ATHENS (Reuters) - A warning by Greece's central bank that the country risked being driven from the euro zone and, ultimately, the European Union failed to break a deadlock with creditors before a potentially decisive meeting of European finance ministers. A top Greek negotiator told Reuters Athens was ready to make unspecified concessions, but once again ruled out any cuts to pensions - a major sticking point in the negotiations. Athens has until the end of June to find a way out of the impasse before it faces a 1.6 billion euro ($1.8 billion)repayment due to the International Monetary Fund, potentially leaving it bankrupt and teetering on the edge of the euro zone.