Greece’s embattled finance minister Yanis Varoufakis stepped up his war of words with eurozone policymakers, saying he wished his country still had the drachma, and would not sign up to any bailout plan that would send his country into a “death spiral”.

With Greece facing a severe cash crisis as it struggles to secure a rescue deal from its creditors, Varoufakis – who has been officially sidelined from the debt negotiations – told a conference in Athens that he would reject any agreement in which “the numbers do not add up”.

“I wish we had the drachma, I wish we had never entered this monetary union,” Varoufakis said. “And I think that deep down all member states with the eurozone would agree with that now. Because it was very badly constructed. But once you are in, you don’t get out without a catastrophe.”

He also warned that a mooted proposal for a bond swap, to ease Athens’ cash-crunch, was likely to be rejected, because it struck “fear into the soul” of European Central Bank president Mario Draghi.

Despite his comments, Greece offered a concession to its international lenders by pushing ahead with the sale of its biggest port, Piraeus.

Greece has asked three firms to submit bids for a majority stake in the port, a senior privatisation official told Reuters, unblocking a major sale of a public asset as creditors demand economic reforms from Athens.

Draghi, who was in Washington to deliver a lecture on monetary policy, pointedly failed to mention the ongoing Greek crisis.

He received a rapturous welcome from Christine Lagarde, the managing director of the International Monetary Fund, who introduced him as “maestro” – the nickname once given to Federal Reserve chairman Alan Greenspan.

“Those who know you understand that you are a man of outstanding insight, fierce determination, and above all, courage. You can call a spade a spade without putting any of your cards on the table,” she said.