Tourists visit the ancient Acropolis hill, with the ruins of the Parthenon temple in Athens.

An International Monetary Fund study published on Tuesday showed that Greece needs far more debt relief than European governments have been willing to contemplate so far, as fractious parties in Athens prepared to vote on a sweeping austerity package demanded by their lenders.

The IMF's stark warning on Greece's debt came as Prime Minister Alexis Tsipras struggled to persuade deeply unhappy leftist lawmakers to vote for a package of austerity measures and liberal economic reforms to secure a new bailout.