By John O'Donnell FRANKFURT (Reuters) - Euro zone central bank chiefs kept their existing cap on a funding lifeline to Greece in place on Wednesday, the ECB said, a move that keeps pressure on Greece as its lenders run out of cash. The Governing Council of decision makers has pared back support to a bare minimum ahead of a bailout referendum that could decide Greece's future in the euro, but decided against cutting it further, for fear that it would further destabilise the banks. As the central bankers gathered in Frankfurt, a defiant Prime Minister Alexis Tsipras urged Greeks to reject an international bailout deal, wrecking any prospect of repairing relations with Europe before the Sunday vote.