(Reuters) - 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.

"During their communication, they expressed their common will for a steady communication throughout the course of negotiations in order to have a mutually beneficial solution soon," said the official, who declined to be named.

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.

But during a regular meeting at the Latvian capital of Riga on Friday, euro zone finance ministers warned its government that it would get no fresh aid until it agreed to a complete economic reform plan.

The official said that the technical teams from Greece and its creditors -- the so-called Brussels Group -- would hold a teleconference on Monday and convene on Wednesday to speed up negotiations.

Three months of fruitless negotiations have raised tensions between Greek Finance Minister Yanis Varoufakis and euro zone colleagues in Riga on Friday.

Euro zone ministers - the so-called Eurogroup - bemoaned talks they felt "were going nowhere" and one minister said that maybe it was time governments prepared for the plan B of a Greek default.

Responding to reports that he was isolated in debt talks, Varoufakis tweeted a quotation by American statesman Franklin Roosevelt on Sunday which read "they are unanimous in their hate for me; and I welcome their hatred."

Varoufakis said the quote expressed his feelings in recent days.

(Reporting by Angeliki Koutantou; Editing by Ralph Boulton)