The chief negotiator for Greece's private creditors said Sunday he remained confident that a deal could be reached on a debt swap plan to slash Athens' debt as the country races against the clock to avoid a messy default.

Greece and its private creditors are converging toward a deal but many details are still unresolved, sources close to the negotiations said during the weekend.

We are at a crossroads and I remain quite hopeful, Institute of International Finance chief Charles Dallara told Antenna TV Sunday.

Athens needs a deal in the coming days to stay afloat when a major debt redemption comes due in March.

After several rounds of talks from Wednesday to Friday, Dallara and special advisor Jean Lemierre left Athens on Saturday without having finalised the deal, with sources saying talks are converging toward private creditors accepting to take a real loss of 65 to 70 percent.

Much of the attention will now turn to a meeting of euro zone finance ministers Monday, and to whether EU states and the IMF consider that the deal that is being put together by Athens and bankers does put Greece's debt back on a sustainable track.

One key question will be whether the deal attracts a big enough participation rate.

We are working together with the Greek government, European and global leaders and we can mobilise very very high participation, Dallara said.

(Reporting by Lefteris Papadimas; Writing by Ingrid Melander; Editing by Maria Golovnina)