CAIRO (AP) — Deadly clashes broke out during funerals of slain supporters Egypt’s ousted Islamist president Sunday, as the leader of the Muslim Brotherhood urged his supporters to stand fast after more than 70 of them were killed in weekend violence.
Setting the stage for more confrontation, the military-installed interim president gave the prime minister the power to grant the military the right to arrest civilians in what government officials said could be a prelude to a major crackdown on Mohammed Morsi’s supporters or Islamic militants who have stepped up attacks against security forces in the Sinai Peninsula.
The extent of the bloodshed has dashed hopes of reconciliation between the country’s two camps, sharply divided over the July 3 military coup that removed Egypt’s first freely elected president following protests by millions of Egyptians demanding he step down.
Islamists staunchly reject the new leadership and insist the only possible solution to the crisis is to reinstate Morsi. Meanwhile, the interim leadership is pushing ahead with a fast-track transition plan to return to a democratically elected government by early next year.
Egypt’s interior minister, who in charge of the police, also pledged to deal decisively with any attempts to destabilize the country, a thinly veiled warning to Morsi supporters occupying two squares in Cairo in a monthlong stand-off with security forces.
The international community, meanwhile, urged restraint.
U.S. Secretary of State John Kerry issued a strongly worded statement on Saturday, saying he told Egyptian authorities it is ‘‘essential’’ they respect the right to peaceful protest. He called on all sides to enter a ‘‘meaningful political dialogue’’ to ‘‘help their country take a step back from the brink.’’
The worst bout of violence since Morsi’s ouster took place before dawn on Saturday when police and armed men in civilian clothes opened fire on his supporters as they sought to expand their sit-in camp by moving onto a nearby main boulevard.
Authorities conceded that the vast majority in Cairo of the 72 killed were demonstrators, but the Interior Ministry said some policemen also were wounded as the military-backed administration sought to defend the bloodshed.
Officials from Morsi’s Brotherhood and their allies decried what they called a new ‘‘massacre’’ against their side, which occurred only weeks after July 8 clashes with army troops in Cairo that left more than 50 Morsi supporters dead.
Civilians, sometimes with weapons, frequently join police in Cairo demonstrations. In some cases, they appear to be plainclothes police; in others residents who back the security forces.
A video posted Sunday on social networking sites show policemen and men in civilian clothes pointing their rifles at the protesters wearing industrial helmets and homemade body armor and standing behind makeshift barricades.
Another video, posted by the Interior Ministry, shows protesters hurling stones and firebombs at the security forces from behind their barricades. One masked man was shown shooting at the police with what appeared to be a large silver-plated pistol.
The authenticity of the videos could not be independently verified, but they generally conformed with Associated Press reporting.
No army troops were on the scene, but the international community and human rights groups expressed concern that the military had allowed the carnage to occur.
Human Rights Watch said many of those killed over the weekend were shot in the head or chest and the killings took place over several hours. The New York-based group said it spoke to witnesses and reviewed extensive video footage of the events. Medical staff, it said, judged some of the deaths to be targeted killings because the position of the shots would likely result in death.
The clashes broke out hours after millions responded to a call by military chief Gen. Abdel-Fattah el-Sissi to take to the streets in a show of support to provide a mandate for him and the police to tackle violence and ‘‘potential terrorism.’’
Two other men were killed and scores injured in violence that followed the funerals of two Morsi supporters Sunday in two cities north of Cairo, Kafr el-Zayat and Port Said.
Mohammed Badie, the supreme leader of the Morsi’s Muslim Brotherhood, launched a stinging attack on el-Sissi over the latest violence, saying the military chief was leading a ‘‘bloody regime’’ and urging his followers to stand fast.
‘‘Don’t be sad and don’t despair,’’ he said in a message to followers posted on his website.
The Brotherhood rejects the July 3 coup, saying it has overturned a democratically elected administration and refuses to join the post-Morsi political process sponsored by the military. It says security forces were not provoked when they opened fire on its supporters early on Saturday.
Interior Minister Mohammed Ibrahim, who is the only member of Morsi’s former Cabinet to keep his post, accused the pro-Morsi side of provoking bloodshed to win sympathy and suggested that authorities could move against the two main pro-Morsi protest camps: one outside the Rabaah al-Adawiya mosque in eastern Cairo and another in Nahda Square near the main campus of Cairo University.
‘‘I assure the glorious people of Egypt that the police are determined and capable to maintain security and safety to their nation with the support of the sincere sons of the country,’’ Ibrahim said Sunday during a graduation ceremony at the national police academy. ‘‘We will very strongly and decisively deal with anyone who attempts to undermine stability.’’
He depicted the two encampments as a danger to the public, pointing to a string of nine bodies police have said were found nearby in recent days. Some had been tortured to death, police have said, apparently by members of the sit-ins who believed they were spies.
‘‘Soon we will deal with both sit-ins,’’ Ibrahim said.
U.N. Secretary-General Ban Ki-moon also asked security forces to ‘‘act with full respect for human rights’’ and demonstrators to ‘‘exercise restraint.’’
Catherine Ashton, the EU’s foreign policy chief, was due in Egypt later on Sunday and will meet Egyptian leaders on Monday, according to an official statement issued in Cairo. It will be her second visit to Egypt this month, a sign of the alarm felt in the West over the continuing bloodshed in the country.
The U.N.’s human rights chief Navi Pillay issued also condemned the violence and called for a ‘‘credible, independent investigation’’ into the killings.
‘‘Despite all the warnings, all the calls for restraint, more than 150 Egyptians have died during protests over the past month, not just in Cairo but in other cities as well,’’ she said. ‘‘I fear for the future of Egypt if the military and other security forces, as well as some demonstrators, continue to take such a confrontational and aggressive approach. Supporters of the Muslim Brotherhood have the right to protest peacefully like anyone else.’’
Associated Press writers Maggie Michael in Cairo and Frank Jordans in Berlin contributed to this report.