CAIRO — Egypt descended deeper into political turmoil on Thursday as the embattled president, Mohammed Morsi, blamed an outbreak of violence on a ‘‘fifth column’’ and vowed to proceed with a referendum on an Islamist-backed constitution that has prompted deadly street battles between his supporters and their secular opponents.
As the tanks and armored vehicles of an elite military unit ringed the presidential palace, Morsi gave a nationally televised address offering only a hint of compromise, while preserving his assertion of sweeping authority. His opponents quickly rejected, even mocked, his speech and vowed continued protests ahead of a planned Dec. 15 vote on the draft constitution.
Many said the speech had echoes of his predecessor, Hosni Mubarak, who saw conspiracy in the unrest that brought him down. Morsi said that corrupt beneficiaries of Mubarak’s autocracy had been ‘‘hiring thugs and giving out firearms, and the time has come for them to be punished and penalized by the law.’’ He added, ‘‘It is my duty to defend the homeland.’’
Morsi, a former leader of the Muslim Brotherhood, spoke a day after the growing antagonism between his supporters and the secular opposition had spilled out into the worst outbreak of violence between political factions here since Gamal Abdel Nasser’s coup six decades ago. By the time the fighting ended, six people were dead and hundreds wounded. The violence also led to resignations that rocked the government, as advisers, party members, and the head of the commission overseeing a planned vote on a new constitution stepped down, citing the bloodshed and the president’s management of the political crisis.
Morsi also received a phone call from President Obama, who expressed his ‘‘deep concern’’ about the deaths and injuries overnight, the White House said in a statement. ‘‘The president emphasized that all political leaders in Egypt should make clear to their supporters that violence is unacceptable,’’ the statement said, chastising both Morsi and the opposition leaders for failing to urge their supporters to pull back during the fight.
Prospects of a political solution also seemed a casualty, as both sides effectively refused to back down on core demands.
The opposition leadership refused to negotiate until Morsi withdrew a decree that put his judgments beyond judicial review — which he refused to do. And it demanded that a referendum on a new constitution be canceled, which he also refused.
The hostilities have threatened to undermine the legitimacy of the constitutional referendum with doubts about political coercion. The feasibility of holding the vote also appears uncertain amid attacks on party offices around the country and open street fighting in the shadow of the presidential palace.
Though Morsi spoke of opening a door for dialogue and compromise, leaders of the political opposition and the thousands of protesters surrounding his palace dismissed his conspiratorial saber rattling as an echo of Mubarak. And his tone, after a night many here view as a national tragedy, seemed only to widen the gulf between his Islamist backers and their secular opponents over his efforts to push through the referendum on an Islamist-backed charter approved over the objections of most liberal factions and the Coptic Christian church.
Outside the palace, demonstrators huddled around car radios to listen to Morsi’s words and mocked his attempts to blame outside infiltrators for the violence, which began when thousands of his Islamist supporters rousted an opposition sit-in.
‘'So we are the ones who attacked him, the ones who attacked the sit-in?’’ one protesters asked sarcastically. ‘‘So we are the ones with the swords and weapons and money?’’ asked another.
Some left for the headquarters of the Muslim Brotherhood, where a mob had broken in, looted offices, and made a bonfire out of the belongings of the group’s spiritual leader — until riot police officers chased them away with tear gas.
“I never thought I would say this, but even Mubarak was more savvy when he spoke in a time of crisis,’’ said Hossam Bahgat, executive director of the Egyptian Initiative for Personal Rights.
The director of state broadcasting resigned Thursday, as did Rafik Habib, a Christian who was the vice president of the Muslim Brotherhood’s Freedom and Justice Party and the party’s favorite example of its commitment to tolerance and pluralism. Their departures followed an announcement by Zaghoul el-Balshi, the new general secretary of the commission overseeing a planned constitutional referendum, that he was quitting.
Morsi’s speech, previously set for 6 p.m. here and delayed for several hours, was his first attempt to address both the night of deadly violence and the underlying crisis set off by his Nov. 22 decree putting his own edicts above the review of any court until the ratification of a new constitution. He has said he needed those powers to protect the constitutional assembly and planned referendum. He said he wanted to head off interference by a counterrevolutionary conspiracy of corrupt businessmen and foreign enemies, cynical opposition leaders willing to derail democracy rather than let Islamists win elections, and the Mubarak-appointed judges who had already dissolved an earlier assembly and the democratically elected Parliament.
Each side of the political battle is now convinced that it faces an imminent coup. Secular groups believe Morsi is forcing through a constitution that will ultimately allow Islamist groups and religious leaders to wield new power. And the demands to stop the referendum have persuaded Islamists that their secular opponents seek to abort the new democracy.
Advisers to Morsi say he has sought for days to find a way to reach out to his critics and resolve the building tension. In his speech, he offered to withdraw an article of his recent decree whose Orwellian language giving him ill-defined powers to protect the revolution had unnerved his opponents. He invited opposition and youth leaders to join him for a meeting at his palace at 12:30 p.m. on Saturday.