ATHENS — In an unexpected move, Prime Minister Alexis Tsipras went on national television early Saturday to call for a referendum on July 5, so that Greek citizens can decide whether to accept or reject the terms of a bailout deal proposed by the country’s creditors.

With his speech, Mr. Tsipras upends the stalemate in negotiations between Greece and its creditors, throwing into doubt whether Greece will be able to make a 1.6 billion euro debt payment that is due on Tuesday to the International Monetary Fund, while also deepening concerns that the beleaguered country could leave the eurozone.

Mr. Tsipras said he was calling the referendum because Greece’s creditors — the I.M.F., the European Central Bank and the eurozone countries — had refused to negotiate in good faith and present a fair compromise.

“After five months of tough negotiations, our partners ended up with a proposal in the form of an ultimatum,” Mr. Tsipras said, arguing that the creditors were calling for “new, unbearable measures,” including cuts to pensions, salaries and tax increases.