Foes dismissed Egyptian President Mohamed Morsi\'s dialogue plea and called for new protests Friday after Morsi blamed a subversive alliance for deadly clashes. Many opposition leaders refused to engage in Morsi\'s proposed \"national dialogue\" until Morsi withdraws a Nov. 22 decree that gave him sweeping powers to legislate without oversight of any court, removing the last check on his authority. They also insisted a Dec. 15 constitutional referendum Morsi ordered be canceled. They accused Morsi and the Islamists of seeking to establish a new dictatorship, in part by ramming through a rushed constitution they charge could give new power over society to Muslim scholars and Islamists groups. Morsi has said he needs the expanded powers to block a conspiracy by corrupt businessmen, opposition leaders and judges appointed by ousted President Hosni Mubarak to thwart Egypt\'s transition to a constitutional democracy. Morsi repeated Thursday night in a nationally televised speech he would keep his powers through the referendum, which he insisted would be held as scheduled. But he offered to meet with opposition and youth leaders at the presidential palace in downtown Cairo Saturday to try to hammer out a compromise that might include adjustments to the constitution. He additionally said in his address even if the constitution failed Dec. 15, he would relinquish his emergency powers. Morsi called Wednesday night\'s bloody clashes between his Islamist backers and liberal, secular and other opponents -- which killed at least seven people and wounded more than 700 -- the work of \"infiltrators\" inside the opposition. He spoke of a \"fifth column\" of people who are clandestinely undermining the nation from within and said some protesters had been paid and armed to perpetrate \"thuggery\" and \"terrorism.\" \"The time has come for them to be punished and penalized by the law,\" Morsi said, adding, \"It is my duty to defend the homeland.\" His speech was immediately followed by violence, The Wall Street Journal and BBC reported. The Cairo headquarters of the Muslim Brotherhood, the powerful Islamist organization Morsi once led, was set on fire, the group said. There were no immediate reports of injuries. Some opponents told The New York Times Morsi\'s speech had echoes of Mubarak, who always saw \"hidden hands\" behind public unrest. Other opposition leaders called Morsi\'s offer all but meaningless, the Times said. Egypt\'s influential al-Azhar University, one of the world\'s chief centers of Islamic learning, called on Morsi to rescind the decree. As violence raged Friday and protests were planned, the presidential palace was ringed by barbed wire, tanks and armored vehicles of the elite Republican Guard, the army\'s senior-most division. The White House said President Barack Obama called Morsi to express his \"deep concern\" about the protesters\' deaths and injuries and welcomed Morsi\'s call for a dialogue, which Obama said \"should occur without preconditions.\" Obama \"emphasized that all political leaders in Egypt should make clear to their supporters that violence is unacceptable,\" the White House said.