CAIRO -- An angry Mohammed Morsi refused yesterday to call off a referendum on a disputed constitution that has sparked Egypt's worst political crisis in two years, drawing chants of "topple the regime!" from protesters who waved their shoes in contempt.

The president's uncompromising stand came a night after pitched battles outside his Cairo palace left at least six dead and 700 injured.

Speaking in a nationally televised address, Morsi accused some in the opposition of being remnants of Hosni Mubarak's authoritarian regime and vowed he would never tolerate anyone working for the overthrow of his "legitimate" government.

That brought shouts of "the people want to topple the regime!" from the crowd of 30,000 opponents -- the same chant used in the protests that brought down Mubarak.

Morsi invited the opposition to a "comprehensive and productive" dialogue starting Saturday in his presidential palace, but gave no sign of offering any meaningful concessions.

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The opposition has already refused to engage Morsi unless he first rescinds decrees giving him nearly unrestricted powers and shelves the draft constitution hurriedly adopted by his Islamist allies last week.

Morsi said the referendum on the disputed charter would go ahead as scheduled on Dec. 15. As he spoke, Morsi wore a black tie in mourning for six people killed in Wednesday's clashes.

President Barack Obama called Morsi to express "deep concern" about the deaths and injuries of protesters.

Earlier, another Morsi adviser quit to protest his handling of the crisis, the seventh of those in his 17-person inner circle who have abandoned him.

-- AP