IMF chief Christine Lagarde and ECB president Mario Draghi unexpectedly joined the leaders of France and Germany as well as European Commission head Jean-Claude Juncker in Berlin late Monday for urgent talks on Greece's debt crisis, diplomatic sources said.

The aim of the late-night meeting attended by German Chancellor Angela Merkel and French President Francois Hollande was to come up with "a final proposal" to present to Athens, according to German daily Die Welt, as the cash-strapped country remains locked in tough negotiations with creditors.