President Barack Obama and German chancellor Angela Merkel spoke on Sunday and agreed it is “critically important” to find ways to keep Greece in the eurozone, the White House said.

About Obama’s conversation with Merkel, the White House said in a statement: “The leaders affirmed that their respective economic teams are carefully monitoring the situation and will remain in close touch.

“The two leaders agreed that it was critically important to make every effort to return to a path that will allow Greece to resume reforms and growth within the euro zone.”

On Saturday, US treasury secretary Jack Lew urged European finance ministers and the International Monetary Fund to continue working together toward a “sustainable solution” to reforms in Greece and its recovery within the eurozone.

Lew spoke by phone with several top officials on Saturday, including the finance ministers of Germany and France and IMF managing director Christine Lagarde, according to a readout of the call provided by the Treasury Department on Sunday.

In those calls, Lew said it was “important for all parties to continue to work to reach a solution, including a discussion of potential debt relief for Greece, in the run up to the 5 July referendum”, according to the readout.

European Union negotiators broke off bailout talks over the weekend after leftist Greek Prime Minister Alexis Tsipras called a July 5 referendum on the latest offer and urged voters to reject the “humiliation.” French Prime Minister Manuel Valls warned that there was a real risk of Greece leaving the eurozone if voters reject the offer.

“In these critical hours, we must remember that the only thing to fear is fear itself,” Tsipras tweeted late Sunday. “The dignity of the Greek people in the face of blackmail and injustice will send a message of hope and pride to all of Europe.”