As time ticks down for a deal, Athens and the lenders remain at odds over how far Greece is willing to bend to meet demands for austerity in exchange for funds desperately needed to avoid a default. The dispute is likely to come to a head by a European summit on June 25, or possibly earlier, at which either Mr. Tsipras or German Chancellor Angela Merkel may have to back down.

In a speech to Syriza party lawmakers, Mr. Tsipras said that Greece cannot accept deeper austerity demands from its international creditors—other eurozone countries and the International Monetary Fund, accusing them of trying to humiliate the country and the IMF of having “criminal responsibility” for the country’s current economic woes.