on citizens to vote 'no' in the referendum on the constitution," the National Salvation Front, alliance of opposition parties, said in a statement. The Front asked "Egyptians to go to polling stations to refuse the proposed constitution and to vote no."
Earlier, the opposition was demanding that the referendum, due to be held on December 15 and December 22, to be scrapped.
The largely secular opposition, however, set several conditions for it to accept the poll, including that the referendum be held over a single day.
According to Aljazeera, the opposition also demanded that there be full judicial supervision of the process, and that international and local NGOs be allowed to monitor it.
The armed forces, in a statement, said the planned meeting aimed at building national dialogue between political forces, which had been called for by the minister of defence, will be postponed for the time being.
The reason behind the postponement of the meeting was the reluctance of many political actors to respond to the invitation, according to the statement published on the official Facebook page of the spokesperson for the armed forces.
Earlier in the day, Egyptian Central Elections Commission announced that the vote on the draft constitution would be held on two different dates.
It said the vote, initially set only for December 15, will take place both on Saturday and a week later on December 22. Each round will cover a different region, the state media reported.
According to Aljazeera, the two-day voting plan had been adopted because many of the judges needed to oversee the vote were staying away in protest at the decision to hold the referendum, so voting had to be staggered to move the judges around.
Egyptians abroad, meanwhile, have already begun voting in the referendum on the new constitution, state media said. Voting was taking place at Egyptian embassies abroad, with more than 500,000 Egyptians expected to cast their votes in 150 countries.
The present political turmoil began after President Mohamed Mursi granted himself absolute powers through the November 22 decree that had put his decisions beyond judicial review, a move which gained him titles like "dictator" and "Pharaoh".
Mursi tried to calm protests by annulling the decree, but decided to go ahead with the December 15 referendum on a new Islamist constitution as scheduled.
Egypt's Constituent Assembly on November 30 in a marathon session approved a draft constitution imposing Islamic values, a move opposed by Liberals as an attempt to restrict freedom of speech and religion in the country.