United Nations envoy to Zimbabwe, Haile Menkerios, says he expects President Robert Mugabe and opposition leader Morgan Tsvangirai to sign an agreement about negotiations within the next 24 hours.
The ABC reports it had been hoped the agreement, which would set an agenda for talks, would be signed on Sunday.
Mr Mugabe, 84, won a one-man presidential election last month. He has ruled since independence in 1980.
The MDC has refused to recognise the election result.