European Central Bank executive board member Benoît Cœuré said on Monday it was now possible that Greece may end up exiting the euro zone although this was not what the ECB wanted.It was the most direct admission yet by a top ECB policymaker that a "Grexit" could happen after Athens decided to interrupt talks on an aid-for-reforms package and call a referendum for July 5."A Greek exit from the euro zone, so far a theoretical issue, can unfortunately not be excluded any more," Cœuré told French financial daily Les Echos.Cœuré said that if Greeks vote "Yes" in the referendum, he "has no doubt" euro zone authorities will find ways to meet commitments towards Greece.If the "No" vote wins, "it would be very difficult to resume political dialogue," he said.Cœuré said that the market reaction to the Greek referendum has been relatively mild but that the central bank was monitoring the situation closely and would use all available instruments, or even new ones, if needed.