Tens of thousands of Greeks took to the streets on Friday in rival rallies that laid bare the deep divide heading into a referendum that may decide the country's future in Europe's single currency.

Prime Minister Alexis Tsipras, elected in January on a promise to end years of austerity, urged people packing Syntagma Square in central Athens to spurn the tough terms of an aid deal offered by international creditors to keep the country afloat.

His European partners say a "no" vote will jeopardize Greece's membership of the euro.