Greek Prime Minister Alexis Tsipras and German Chancellor Angela Merkel agreed in a phone conversation on Sunday to maintain contact during talks between Athens and its lenders to reach a debt deal, a Greek government official said. Shut out of international markets and locked in talks with its European Union and International Monetary Fund creditors over its proposed reform-for-cash deal, Greece risks running out of cash within weeks. Three months of fruitless negotiations have raised tensions between Greek Finance Minister Yanis Varoufakis and euro zone colleagues in Riga on Friday.