CAIRO (AP) — They showed a military-style precision: Crowds of bearded Islamists proclaiming allegiance to Egypt's President Mohammed Morsi and chanting "God is great" as they descended on tents set up by anti-Morsi protesters outside the presidential palace, swinging clubs, firing rifles and calling for burning down the opposition. They set up a detention facility, interrogating and beating captured protesters.

The scene from bloody clashes outside the presidential palace a week ago hangs over Egypt's political crisis as a daunting sign of how much more violent the confrontation could become between Morsi's Islamist supporters and the opposition that has launched a giant wave of protests against him.

Opponents of Morsi accuse his Muslim Brotherhood supporters of unleashing highly trained cadres — fired up with religious slogans — to crush their political rivals. They fear last week's violence was a signal that the Brotherhood will use force to push its agenda and defend its political gains in the face of a persistent protest movement demanding that Morsi withdraw a draft constitution largely written by his Islamist allies.

Ahead of new mass rallies by both sides Tuesday, masked gunmen attacked anti-Morsi protesters in Cairo's central Tahrir Square before dawn, firing birdshot at them and wounding nine. It was unclear who was behind the attack, said security officials, speaking on condition of anonymity because they were not authorized to talk to the press.

Officials from the Brotherhood and its political party deny using violence to quell critics. Regarding the clashes last Wednesday, the worst violence yet in the crisis, they say Morsi supporters were defending the palace and accuse the protesters of starting the battles. They claim their side suffered more deaths and injuries during the clashes, which left at least eight people dead. More broadly, the Brotherhood accuses former regime supporters of paying thugs in an organized campaign to topple Islamists from power, pointing to a series of attacks on Brotherhood offices the past weeks.

Story continues

"The group and the party don't use violence and have no inclination to the use of violence," said Mourad Aly, a Brotherhood party spokesman. He added, "We will never allow an attack or breach on the palace."

However, when last week's violence began, the only protesters outside the palace were several dozen people conducting a sit-in in the tents, and the allegiances of those killed remain controversial. Opponents and rights lawyers charge that the Brotherhood has tried to persuade some families to declare their deceased sons as Brotherhood.

Testimonies and videos that have emerged from the nearly 15 hours of street clashes show an organized group of disciplined Islamists, working in units and carrying out military-type exercises as they broke up the tent sit-in at the palace.

In one video posted online, thousands of Islamists lined up on a main boulevard near the palace, chanting "Power, Resolve, Faith, Morsi's men are everywhere," and chanting calls of burning down the opposition — then they assaulted the camp.

The exact circumstances of the online videos could not be independently confirmed, but their contents were consistent with Associated Press reporting.

Opponents of the Brotherhood frequently accuse the group of running a "militia." The group is known for its tight discipline, and it acknowledges that many of its young members undergo organized martial arts training — but it vehemently denies forming any militias.

Tharwat el-Kherbawy, a former Brotherhood member and now an opponent of the group, said the Brotherhood's central organizational doctrine — calling on members to "hear and obey" their leaders — gives it a military-like structure.

When the Brotherhood met a stronger than expected protest movement, "they had no hesitation in hastening to implement their ideas and resorting to violence," he said. "If their empowerment project is facing resistance, this resistance must be quelled."

The Dec. 5 showdown was the fiercest display of the Brotherhood's strength, but similar, smaller attacks on opponents by Brotherhood members took place at least three times earlier this year when secular and liberal groups criticized the Brotherhood's grip on power.

During last Wednesday's fighting, nearly 140 anti-Morsi protesters were tortured and interrogated at a makeshift detention center set up by the Brotherhood along the walls of the presidential palace, according to witnesses. The detained protesters were filmed making forced confessions that they had received foreign funds, according to some who were held and an Egyptian journalist who snuck into the site.

One of the victims, Yehia Negm, an Egyptian diplomat, told AP he was dragged on the ground to the center where he was beaten. He is suffering from multiple injuries in the head, eye, nose, and ribs from beating and had remains of pellets in his forehead from gunfire during the clashes.

"When they found my ID that says a diplomat, they started accusing me of working with security agencies, of being a spy and of serving foreign countries," Negm said. "They rained beatings down on me. They started yelling at me, saying, 'You infidels, you want to burn the country down, you are not Muslims.'"

Around 20 Islamists manned the center, made up of metal barricades erected against the palace wall, said Mohammed Elgarhy, a local journalist with the daily Al-Masry Al-Youm who snuck in and spent nearly four hours there. Among them was a man he recognized as a well-known Brotherhood lawyer and two others he overheard speaking with a Brotherhood leader. The others, who he said he believed were Brotherhood members, carried out the beatings and interrogations.

"The Brotherhood were carrying out the job of the Interior Ministry," Elgarhy told AP. "They would arrest anyone they suspected ... asking them questions such as who paid for you to come here."

Troops from the Central Security Forces guarded the site, but did not interfere, he said. The Brotherhood has not addressed accusations about the detention center but says it did seize protesters and hand them over to police.

The violence came a day after hundreds of thousands marched on the palace in Cairo's upper middle class district of Heliopolis, demanding Morsi withdraw the draft constitution and sweeping powers that he had given himself in a series of decrees.

After the rally, several dozen protesters remained in the tent camp. In response, the Brotherhood called a "general mobilization" of its members, and its spokesman said the group will protect the legitimacy of the president and state institutions.

The next day, last Wednesday, the lines of Islamists stormed the camp, chanting "God is great" and "Islamic law is fundamental in Egypt," as they tore down tents and chased away the protesters. They then ransacked the tents. Brotherhood supporters claimed they found evidence of drug use at the camp — though they never showed any — and that burnt charcoal and processed cheese in the tents proved the protest was foreign funded, without explanation. The accusations were reminiscent of those leveled by the regime of ousted President Hosni Mubarak against the protesters who rose up against his rule in early 2011.

As news of the attack spread, more anti-Morsi protesters arrived on the scene. Buses, seen parked nearby, brought in Brotherhood supporters. By sunset a full-fledged street battle transformed Heliopolis into a war zone, spreading over at least three fronts near the palace. Protesters and witnesses put the number of Morsi supporters at up to 12,000 compared to several thousand protesters.

At the height of the fighting, leading Brotherhood member Essam el-Erian went on Misr 25, a TV station affiliated with the group to call on Morsi supporters to go to the scene "in the tens of thousands to besiege those thugs because now is the moment to arrest them" and expose the conspiracy. He called the protesters counter-revolutionaries who want to carry out "a coup against legitimacy."

Bearded men in short robes waved sticks in the air as they chased groups of young men and women down darkened alleys while gunfire echoed in the background.

A resident of a building overlooking one front line said Morsi supporters appeared to be operating by what a well-rehearsed plan. They came prepared with metal sheets for barricades and motorcycles with small trailers attached brought loads of stones to pelt protesters with. The resident spoke on condition his name not be used for fear of retribution.

Some Morsi supporters were armed with rifles, firing from the edges of the front lines to avoid being detected, said Mahmoud Zaghloul, a 22-year old protester who got hit with a rock in his head. He also said many in the Morsi camp came prepared with helmets with plexi-glass face screens.

At least one video shown on a private TV station shows a man in the Morsi camp, wearing a full helmet, taking a professional shooter position, bending his knees and aiming with a rifle.

"One of the most disturbing things was how they chanted 'God is Great' as they aimed at us," as if they were firing at infidels, Zaghloul said.

Some in the anti-Morsi camp also had firearms, witnesses said. At least one amateur video circulating online that showed an anti-Morsi protester pointing a pistol from behind a barricade at the opposing camp.