CAIRO — An angry Mohammed Morsi refused Thursday 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 Egyptian president’s uncompromising stand came a night after thousands of his supporters and opponents fought pitched battles outside his Cairo palace, leaving at least six dead and 700 injured.

Speaking in a nationally televised address, Morsi accused some in the opposition of serving 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 Morsi opponents — the same chant used in the protests that brought down Mubarak.

Morsi also invited the opposition to a “comprehensive and productive” dialogue starting Saturday at his presidential palace, but gave no sign that he might offer any meaningful concessions.

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 in a marathon session last week.

Morsi said the referendum on the disputed charter would go ahead as scheduled on Dec. 15. He also refused to rescind the Nov. 22 decrees.

Reading from prepared notes, Morsi frequently broke off to improvise. He wore a black tie in mourning for the six people killed in Wednesday’s clashes.

Earlier Thursday, Morsi’s troubles grew when another of his advisers quit to protest his handling of the crisis, raising the number of those in his 17-person inner circle who have abandoned him to seven. The only Christian in a group of four presidential assistants has also quit.

Violence persisted into the night, with a group of protesters attacking the Cairo headquarters of Morsi’s Muslim Brotherhood, ransacking the ground floor. Another group of protesters attacked the Brotherhood’s offices in the Cairo district of Maadi. Outside the president’s house in his hometown of Zagazig, 50 miles north of Cairo, police fired tear gas to disperse hundreds of protesters, security officials said.

During his speech, Morsi repeated earlier assertions that a conspiracy against the state was behind his move to assume near unrestricted powers, but he did not reveal any details of the plot.

“It is my duty … to protect institutions of the nation,” he said. “I will always fulfill this role, no matter how much pressure or what the situation.”