The political struggle over a divisive new constitution for Egypt went into campaign mode on Thursday with Islamists backing President Mohammed Morsi and the opposition urging either support or rejection of the draft charter.

The staggered referendum to decide the text is to begin on Saturday across half of Egypt, including in Cairo and Alexandria. The rest of the country will vote a week later, on December 22.

An Egyptian journalist who was hit in the head by a rubber bullet while covering bloody clashes in Cairo last week has died in hospital from his injuries, the state MENA news agency reported on Wednesday.

El-Husseini Abu Deif, a reporter for the al-Fajr independent news weekly, had been in a coma with a fractured skull and severe brain injury, it said.

Egypt's crisis showed no sign of easing on Wednesday as the army delayed unity talks meant to ease political divisions and the opposition set near-impossible demands for not boycotting a constitutional referendum.

Voting on the controversial Islamist-backed draft charter is due to start on Saturday, with a second round scheduled for a week later following a last-minute decision by the electoral commission to spread polling over two days.

Egypt's referendum on a controversial draft constitution will now take place on two separate dates, Egyptian state television said on Wednesday.

The electoral commission announced that the vote, initially set only for December 15, will take place both on Saturday and a week later on December 22, Nile TV said.

The United States warned Tuesday there must be no return to the "bad old days" of the Mubarak era in Egypt, as the army there called for talks to resolve a crisis over a constitutional referendum.

"We continue to have deep concerns about the situation in Egypt," State Department spokeswoman Victoria Nuland said.

Egypt's powerful army called for President Mohamed Morsi and the secular opposition to meet to resolve a deepening crisis over a constitutional referendum as the rival camps organized mass protests Tuesday.

General Abdel Fattah al-Sissi, the country's armed forces chief and defense minister, made the appeal "for the sake of Egypt" to all political groups and movements to meet on Wednesday at a Cairo military sports complex, according to a statement posted on the military's official Facebook page.

Egypt's powerful army called for President Mohamed Morsi and the secular opposition to meet to resolve a deepening crisis over a constitutional referendum that sparked rival mass protests on Tuesday.

General Abdel Fattah al-Sissi, the country's armed forces chief and defense minister, made the appeal "for the sake of Egypt" for all political groups and movements to meet on Wednesday at a Cairo military sports complex, according to a statement posted on the military's official Facebook page.

President Mohammed Morsi has ordered Egypt's army from Monday to take on police powers -- including the right to arrest civilians -- in the run-up to a vote on a constitution that has triggered bloodshed.

The decree takes effect on the eve of mass rival protests on the referendum that is to be staged on Saturday, and follows street clashes that have left seven people dead and hundreds injured.

Egyptian Islamist movements, including President Mohamed Morsi's Muslim Brotherhood, will hold a rival demonstration on Tuesday, the same day as protests organised by the opposition, a Brotherhood spokesman told Agence France Presse.

A coalition called the Alliance of Islamist Forces "is calling for a demonstration Tuesday under the slogan 'Yes to legitimacy'," in support of a constitutional referendum championed by Morsi, Mahmud Ghozlan said.

Arab League chief Nabil al-Arabi hoped on Sunday that the United States and Russia could reconcile their views over Syria in order to facilitate a settlement of the crisis in the war-ravaged country.

"Talks between the United States and Russia along with the international envoy (Lakhdar Brahimi) continued in Geneva today," Arabi told a meeting of the Arab ministerial committee on Syria held in Doha.