"We are extremely worried," said Khaled Dawoud, a spokesman for the main opposition coalition, the National Salvation Front. "We feel threatened and we expect the worst," he told The Associated Press.
Egypt's ongoing tug of war pits Morsi, a Brotherhood veteran, and his Islamist allies in one camp against a mostly secular and liberal opposition backed by moderate Muslims, minority Christians and a large segment of women in the other.
The opposition charges that Morsi and the Brotherhood have failed in tackling any of the nation's most pressing problems and are trying to monopolize power, renegading on promises of inclusiveness. Morsi blames the country's woes on nearly three decades of corruption under his predecessor, Hosni Mubarak, and accuses the opposition of stoking unrest for political gain.
Friday's clashes outside the Brotherhood's headquarters were the worst in more than three months between the Brotherhood and protesters.
The violence was rooted in an incident a week earlier, when Brotherhood members slapped a woman to the ground and beat up other activists who were spray-painting graffiti against the group outside its headquarters, in an eastern district of Cairo. Several reporters at the scene were also attacked. The Brotherhood said they were part of the protest.
In response, anti-Brotherhood activists called for a protest there Friday to "restore dignity." Both sides brought out hundreds of supporters, and the scene quickly turned to mayhem, with beatings committed by both sides. Images of bloodied men, others being dragged on the streets, fires in the street and cars in flames were splashed on news pages on Saturday and Sunday. More than 200 people, from both sides, were injured.
Brotherhood officials accused the protesters of attacking its office, saying its members were defending the building. Protesters, in turn, blame Brotherhood members for the violence.
In a speech Sunday, a visibly angry Morsi, shouting and pounding the table, warned his opponents, saying he may be close to taking unspecified measures to protect the nation.
"There has to be clear distinction between political practice and the freedom of expression and violence, thuggery and incitement," Pakinam el-Sharqawi, a close Morsi aide, told reporters.
The prosecutors' announcement signaled a wider response beyond protesters to pursue opposition figures.
The arrest warrants Monday were issued against five activists who were at the forefront of the 2011 uprising against Mubarak and a subsequent campaign against the army generals who succeeded him and ruled for nearly 17 months.
They include Alaa Abdel-Fattah, a prominent blogger detained for two months in 2011 over allegations he attacked soldiers carrying out a bloody crackdown on protesters. He was released without charges in that case.
Abdel-Fattah posted a statement on his Facebook account saying the warrants showed the bias of the attorney general in favor of the president. Still, he said he would still surrender to the prosecutor's office on Tuesday.
"I am not afraid of the prisons of a tyrannical state and I will not accept to turn from a person unfairly accused of fabricated charges into a fugitive from justice," he wrote.
Another of the five, Ahmed Douma, was beaten by Brotherhood supporters, his face left bleeding, in the initial incident that sparked Friday's protest.
Karim el-Shaer is also a blogger and a veteran pro-democracy campaigner. Two others Hazem Abdel-Aziz and Ahmed Ghoneimi are prominent members of the opposition al-Dustor Party, led by Nobel peace Laureate and top pro-democracy advocate Mohamed ElBaradei.
The prosecutor also summoned a sixth activist, Nawara Negm, daughter of Egypt's best known satirical poet, for questioning over the same allegations.
"This is a farce and nonsense," Negm told the AP, noting that activists loyal to Morsi had in the past openly called for violence against opponents on social networking sites but were never summoned for questioning. She said she had not received the summons and would not surrender to authorities if she does get one. "The attorney general is illegitimate."
The south Cairo prosecutors' office also summoned several opposition figures for questioning, including former presidential candidate Khaled Ali and former lawmaker Ziad el-Oleimi.
The removal of Talaat Abdullah, the attorney general and top prosecutor, is a key opposition demand. His appointment by Morsi in November caused an uproar among a large number of judges who criticized the move as trampling on their right to pick the top prosecutor. He briefly quit when prosecutors besieged his office demanding his dismissal before he returned to his job.
His Monday statement said a forensic expert will examine four compact discs containing statements and video clips posted on the six activists' Facebook and Twitter accounts. It alleged the material included incitement to burn the offices of the Brotherhood and kill Brotherhood members.
A wider inquiry will examine the contents of social networking sites in the run-up to Friday's clashes.
Activists and rights lawyers pointed out that none of the Brotherhood members involved in Friday's violence has been summoned or slapped with arrest warrants. Three pro-Brotherhood filmed attacking protesters in the initial violence a week earlier were summoned but never questioned.
In the same vein, they noted, none of the president's supporters who set upon peaceful protesters outside the presidential palace on Dec. 5 were ever held accountable or even summoned. The attack on the protesters late last year sparked hours of street clashes in which at least 10 people were killed and hundreds injured while Brotherhood supporters operated a makeshift detention center for opponents. The Brotherhood insists most of the dead were its supporters, a claim disputed by activists.
The Brotherhood's legal adviser, Abdel-Moneim Abdel-Maqsoud, said he had filed complaints with the top prosecutor against a total of 169 individuals, including political party leaders he alleges were involved in Friday's violence.
In his angry address Sunday, Morsi departed from prepared comments at a women's rights conference to deliver a scathing attack against opponents. The president suggested that he may have to resort to "emergency" measures to deal with his opponents. He accused his foes of using paid thugs to sow chaos and the media of inciting violence.
He did not specify any particular opposition group, but vowed he would not allow anyone to undermine the law.
"There is a president of the republic and there are emergency measures if any of them makes even the smallest of moves that undermines Egypt or the Egyptians," he said.
"Their lives are worthless when it comes to the interests of Egypt and Egyptians," he said, pounding on the table. "I am a president after a revolution, meaning that we can sacrifice a few so the country can move forward. It is absolutely no problem."
Morsi also criticized the media, arguing that it was being used for political aims, an accusation made repeatedly by Brotherhood officials in recent weeks.
Dozens of Islamists are currently staging a sit-in outside the studios of TV networks critical of the president.
On Sunday, the Islamists pelted police with rocks and sought to prevent talk show hosts and guests from going in or out of the complex, located in a suburb west of the capital. Police responded with tear gas. The sit-in continued on Monday.
The Cabinet, led by Morsi ally Prime Minister Hesham Kandil, condemned the sit-in protest and violence against network workers, saying it was not the appropriate way to express opinions.