CAIRO, Dec 8 (Reuters) - A coalition of the Muslim Brotherhood and other Islamist groups called on Saturday for a referendum on a draft constitution to go ahead on time on Dec. 15, after liberals who complain that the document is biased demanded a delay in the vote.

The main Islamist coalition "confirmed the need for measures to hold the referendum on time on Dec. 15 without any amendment or delay", a spokesman for the group told a news conference.

Among those who spoke at the news conference, aired live on television, was Khairat al-Shater, who had been the Brotherhood's candidate for president until he was disqualified, a move that thrusted Mohamed Mursi into his place and into office.