Greek Prime Minister Alexis Tsipras called for a speeding up of the process to conclude a reform-for-cash deal with euro zone creditors after talks with German Chancellor Angela Merkel on Thursday, a Greek official said.

The official said the short meeting on the sidelines of a European Union summit in Brussels - their first since Tsipras visited Berlin on March 23 - took place "in a positive and constructive atmosphere".

Euro zone officials say little progress has been made in detailed negotiations on a Greek economic reform program, partly because Athens has denied representatives of its creditors access to state accounting data.

The official gave no details of their discussion but said: "During the meeting, the significant progress made since the Berlin meeting until today was noted. The prime minister asked that the procedures be speeded up so that the Feb. 20 decision, which foresees a first interim agreement by the end of April, be implemented."