Opponents and supporters of Egyptian President Mohamed Morsi have taken to the streets of Cairo, converging on the presidential palace in another day of demonstrations that have gripped the capital.

VOA's correspondent in Cairo, Elizabeth Arrott, says anti-Morsi crowds participating in Friday's demonstrations are furious that the Egyptian leader has refused to call off a disputed constitutional referendum or curb the sweeping powers he granted himself in a decree last month.

Muslim Brotherhood groups supporting Mr. Morsi are also massing, chanting that the country rejects secularism and wants only Islam as the basis of its constitution. Soldiers have erected barricades with concrete blocks and barbed wire around the presidential palace to prevent surging violence that occurred earlier this week.

Opposition leaders said Friday they will not attend Mr. Morsi's proposed “comprehensive” dialogue on Saturday. The Egyptian leader has insisted that dialogue is the only solution to the country's constitutional crisis.

Speaking on national television Thursday, Mr. Morsi said he will not tolerate killings or sabotage. He said seven people were killed outside the presidential palace, with more than 700 others injured during demonstrations this week. The president says 80 people have been arrested for crimes, including the use of firearms, and he described some of the detainees as “hired for money.”

U.S. President Barack Obama spoke with Mr. Morsi by telephone Thursday to voice “deep concern” about the protest deaths and injuries.

A White House statement said Mr. Obama also urged all Egyptian political leaders to make clear to their supporters that violence is unacceptable.

Mr. Morsi said he will form a new advisory panel to write a new draft constitution if voters on December 15 reject the one passed by his Islamist followers last week. Critics say that document was drafted solely by Islamists without opposition input.