Greece's July 5 referendum does not meet non-binding guidelines drawn up by the Council of Europe, notably one recommending that voters have at least two weeks to make their minds up, the human rights watchdog said today.

It said it was also unable to send observers as a result of the short notice.

While there are no automatic legal consequences, the council's view underlines the confusion that many Greeks feel about the hastily-called plebiscite on whether to accept or reject international creditors' proposals for a cash-for-reform deal.

"We are not prejudging the outcome of the referendum," spokesman Daniel Holtgen said.

Holtgen said the council's secretary general, Thorbjorn Jagland, had noted to various media that the guidelines recommended voters know the question at least two weeks before a referendum and that observers be sent to monitor it.

"This isn't possible (given the short notice) and the secretary general confirmed that the COE had not been asked to observe," he said.

Greek Prime Minister Alexis Tsipras announced the election in the early hours of Saturday after a fresh failure to reach agreement with euro zone states and other creditors.

The Council of Europe was one of the multilateral institutions set up in Europe just after World War Two and is not part of the European Union. It focuses on human rights, democracy and the rule of law and has 47 member states.