The world’s most influential Islamist movement is in danger of collapse in the land of its birth — its leaders imprisoned, its supporters slain and its activists branded as terrorists in what many are describing as the worst crisis to confront Egypt’s 85-year-old Muslim Brotherhood.

In the week since Egypt’s new military-backed rulers ordered a brutal crackdown on camps filled with protesters calling for the reinstatement of ousted president Mohamed Morsi, the group that used its organizational muscle to win the country’s first democratic elections, held in late 2011 and early 2012, has been cast into disarray.

Analysts worry that its members, bitter and angry after the deaths of more than 1,000 Morsi supporters in the past week, could abandon the Brotherhood’s decades-long commitment to nonviolence, particularly as its leadership loses its grip on them. Some pro-Morsi demonstrators have been spotted with weapons, and attacks against security forces in the volatile Sinai Peninsula have intensified since Morsi was deposed July 3.

Meanwhile, the movement is battling a level of popular hostility perhaps unprecedented in its history. The Brotherhood’s strategy of confronting the government with sit-ins and marches in recent weeks seems only to have inflamed public opinion.

On Tuesday, Brotherhood supporters vowed that they would not resort to violence as they continued to challenge the interim government installed by the military after Morsi, the group’s standard-bearer, was toppled.

“Our only option is the peaceful method,” Khaled Hanafi, secretary general of the Brotherhood’s Freedom and Justice Party, said at a news conference in Cairo on Tuesday. The detention overnight of the Brotherhood’s “supreme guide,” Mohammed Badie, would not change the group’s approach, he said.

“We regret the arrest of Dr. Badie, but we have chosen a path, and regardless of the sacrifices, we must continue,” Hanafi said.

Badie was interrogated and remanded into pretrial detention Tuesday on a variety of charges, including inciting the killing of protesters outside the Brotherhood’s Cairo headquarters in June. He is also accused of possessing arms, running an illegal gang and assaulting the military. He is scheduled to go on trial with two other Brotherhood leaders this month.

The detention of the Islamist movement’s spiritual leader, whose image was broadcast repeatedly on television after his overnight arrest, seemed to complete the humiliation of the Brotherhood’s leadership. The mass arrests and deaths of its officials have left the group splintered and unable to take coordinated action, analysts say.

An existential crisis

An organization that just two months ago was governing the Arab world’s most populous nation is at risk of falling apart, said Diaa Rashwan, an expert on Islamist movements at Cairo’s al-Ahram Center for Political and Strategic Studies.

“They are facing a really critical moment. They could disappear. And alternatives already exist,” Rashwan said.

The Brotherhood is more than a political or religious group. It has been almost a shadow state in modern Egypt, winning over supporters over the decades with a vast network of charitable services, including dental clinics and thrift shops. It is the “mother of all Islamist movements,” in the words of Shadi Hamid, a Middle East expert at the Brookings Doha Center, having spawned dozens of related groups worldwide since its founding in 1928.

Throughout its history, the Brotherhood has repeatedly clashed with Egypt’s authoritarian governments, enduring arrests, torture and imprisonment. But what’s different now, analysts say, is that it’s battling not only a military-backed government but also the disdain of a broad swath of society. Many Egyptians are irate at Morsi for the country’s economic slide and the rise in crime during his one-year rule. Others complain that the Brotherhood tried to grab power by excluding minority political groups and trying to insulate its decisions from judicial review.

“It’s the first time to see the Muslim Brotherhood in conflict not only with the state — but with the whole of the state, [including] the bureaucracy, and the political elite, and an important part of society. It’s not a limited confrontation,” Rashwan said.

The Brotherhood has traditionally insisted on strict discipline from its followers. But with the leadership severely weakened, it is much less able to execute a strategy.

Ibrahim el-Houdaiby, a political analyst who belongs to a prominent Muslim Brotherhood family but left the organization in recent years, said, “There is no Brotherhood in terms of hierarchy and decision making. All decisions are being taken on a very local, individual level.”

It is not only the current leadership that is being decimated but also, potentially, the future ranks. Among those who have died in the crackdown are Badie’s 38-year-old son, the 17-year-old daughter of Freedom and Justice Party leader Mohamed Beltagy, and Khaled al-Banna, the grandson of the Brotherhood’s founder, Hassan al-Banna. All were shot by security forces over the past week.

In a sign of the disarray, the Freedom and Justice Party announced Tuesday that Badie would be replaced on an interim basis by Mahmoud Ezzat, the organization’s second in command, who is rumored to be abroad. Later in the day, on its Facebook page, the party retracted the announcement and said that only the Brotherhood could release such news.

The fragmentation could have far-reaching consequences, for instance, if the government eventually wants to negotiate with the group. Houdaiby said the government, by trying to destroy the Brotherhood’s leadership, may no longer have a negotiating partner that can keep the group’s followers in line. He said the Brotherhood is already losing control over them.

“It will lose a great part of its members to violent movements,” Houdaiby said.

Campaign against the group

With Egypt becoming increasingly polarized, the Brotherhood’s opponents are cheering signs of the group’s possible demise. Newspapers and television stations have been waging a sustained campaign against the group, labeling the Brotherhood as terrorists and predicting its collapse. On Tuesday, the headline in the liberal Tahrir newspaper, named for the revolution that unfolded more than two years ago in Cairo’s central Tahrir Square, trumpeted: “The End of the Brotherhood.”

The Tamarod movement, which led the massive street demonstrations that culminated in the coup that toppled Morsi, on Tuesday repeated its call to ban the Brotherhood.

Brotherhood figures are not the only ones in the cross hairs, however. Also Tuesday, a lawsuit was filed against Mohamed ElBaradei, who briefly served as Egypt’s vice president after Morsi’s ouster before resigning in protest at the bloodshed last week and leaving the country.

The case was brought by an Egyptian professor, who accused ElBaradei of “betrayal of trust” for quitting his post. Private lawsuits were used extensively under Mubarak, and under Morsi, to tame political opponents.

Amer Shakhatreh and Lara El Gibaly contributed to this report.