CAIRO (AFP) - Egypt's most senior judges announced on Monday they would delegate judicial officers to oversee a referendum on a controversial draft constitution, overriding calls for a boycott amid growing popular unrest.

The judges' decision brings a measure of relief to President Mohamed Mursi even as pressure mounts against him in the streets, with the opposition calling a new protest rally for Tuesday.

The new charter, which was rushed through by the Islamist-dominated constituent assembly after Mursi on November 22 issued a decree expanding his powers, has become the focal point of Egypt's biggest political crisis since the president was elected in June.

Mursi's decree and the adoption of the constitution by an Islamist-dominated panel has polarised Islamist and largely secular forces with Cairo becoming the theatre of mass rival rallies.

The latest demonstration is scheduled for 1400 GMT on Tuesday, when a coalition of opposition groups, including Nobel Laureate Mohamed ElBaradei's party and supporters of former presidential candidate Hamdeen Sabbahi, are to rally outside the presidential palace to oppose the charter and the referendum.

But the Supreme Judicial Council's announcement that judges would after all monitor the December 15 nationwide referendum required for the draft constitution to pass into law comes as a blow to Mursi's opponents, including judges, who had hoped to delegitimise the vote.

Mohammed Gadallah, Mursi's legal aide, told AFP the decision meant that the referendum would after all take place under judicial supervision.

"The largest body responsible for judges is the Supreme Judicial Council," Gadallah said. "They realised they had a responsibility before the nation to supervise.

"This means, it's over," he said when asked whether it was still possible for the vote to be boycotted by judges.

On Sunday, the Judges Club, which represents judges nationwide, said it would not oversee the referendum on the new constitution.

Judicial anger at Mursi's decree, which puts his decisions beyond the review of the courts, rages on however and on Monday judges began an open-ended strike.

The Supreme Constitutional Court (SCC) suspended its work indefinitely due to "psychological and material pressure" following a protest by Mursi supporters which judges said prevented them from delivering a key ruling that might have dissolved the panel that drafted the charter.

They had intended to hold the session in defiance of Mursi's decree, which barred them from making a ruling on the charter or the Islamist-dominated senate. The court had previously disbanded parliament.

Egyptian expatriates will begin voting on the constitution ahead of time, starting on Saturday when embassies will extend their opening hours, foreign ministry spokesman Amr Roshdy said.

The press threw its weight behind the mounting protests against Mursi, with an editorial in daily Al-Shuruq printing: "Beware - fascism is coming."

"When Islamist protesters surround the SCC headquarters and prevent judges from entering, know that the seeds of a fascist state have been sown," it said of Sunday's demonstration outside the constitutional court.

Eleven independent and opposition party newspapers have declared they will not go to print on Tuesday.

The draft constitution, which is to replace the one suspended after president Hosni Mubarak was toppled in early 2011, has been criticised for failing to protect key rights and allowing a stricter interpretation of Islamic law.

Mursi's supporters accuse the opposition judges of being elitist holdouts from the Mubarak-era who oppose Islamists.

Mursi and his supporters have stressed that his new sweeping powers are temporary pending the ratification of the charter by public vote.