Egypt’s military-backed government on Wednesday designated the Muslim Brotherhood a terrorist organization, criminalizing the activities and finances of a movement that rose to power in national elections last year but has been crippled by a government crackdown since a coup in July.

The announcement was a stunning blow to the decades-old Islamist organization, which survived for years in the shadows and in prison cells under then-President Hosni Mubarak but reached the height of political power after his ouster in the 2011 uprising.

With the victory last year of Mohamed Morsi — a former Brotherhood leader — in Egypt’s first democratic presidential election, the movement was poised to realize its Islamist project. But it struggled to govern the country’s vast and bloated bureaucracy, and after Morsi’s ouster, it became the target of a campaign of arrests and killings.

Wednesday’s decree, which accused the Brotherhood of a deadly car bombing outside a security building Tuesday, broadened the government’s authority to move against the group.

Egyptian legal experts said the decree would shutter hundreds of charities and nongovernmental organizations affiliated with the Brotherhood, one of Egypt’s largest opposition groups. The organizations provide health care and other services to rural and urban areas that lack infrastructure.

Anyone who is a member of the Brotherhood, participates in its activities or promotes or funds the group will be subject to prosecution under the Egyptian penal code, analysts said. Membership in a terrorist group is punishable by five years in prison. The maximum penalty for providing weapons and ammunition to a domestic terrorist group is death.

Brotherhood officials could not be reached for comment. But a statement posted on the group’s official Twitter account called Wednesday’s declaration a “worthless decision from an illegal gov’t without any evidence and will not change anything in reality.”

“The protests are in the streets despite a law restricting them — and killings and prison sentences. All this has not changed the will of the people,” said Ibrahim Elsayed, a member of the Brotherhood’s political group, the Freedom and Justice Party, the Associated Press reported. “The decision has no value for us and is only worth the paper it is written on.”

The declaration by Egypt’s interim cabinet seems likely to harden further the divide between Morsi’s supporters and secular backers of the government ahead of a referendum on a new constitution scheduled for next month.

Morsi’s presidency faltered under an already crumbling economy and his controversial efforts to pass a new constitution, further isolating the increasingly unpopular Brotherhood, whose leaders began courting hard-line Islamists to bolster support.

After Wednesday’s announcement, the United States expressed concern about “the current atmosphere and its potential effects on a democratic transition in Egypt.”

“We think it is essential for Egypt to have an inclusive political process; it is the best means of restoring the stability that the Egyptian people want and that is necessary to the country’s economic recovery,” State Department spokeswoman Jen Psaki said. “There needs to be dialogue and political participation across the political spectrum.”

The Egyptian government acted quickly to blame the Brotherhood — which renounced violence decades ago — for the bombing Tuesday in the Nile Delta city of Mansoura. The allegation has inflamed tensions and given rise to vigilante attacks against Brotherhood supporters.

Deputy Prime Minister Hossam Eissa said that, in response to the bombing, the government had decided to classify the organization as a terrorist group. Eissa did not provide evidence that the Brotherhood was involved in the bombing or any other recent attacks on security forces in Egypt.

“Egypt was horrified from north to south by the hideous crime committed by the Muslim Brotherhood group,” Eissa said, according to the AP. “This was in context of a dangerous escalation to violence against Egypt and Egyptians [and] a clear declaration by the Muslim Brotherhood group that it still knows nothing but violence.”

“It’s not possible for Egypt the state nor Egypt the people to submit to the Muslim Brotherhood terrorism,” he added.

On Wednesday, a Sinai-based jihadist group, Ansar Bayt al-Maqdis, or Ansar Jerusalem, claimed responsibility for Tuesday’s bombing, which killed 15 people, including 11 police officers, in one of the deadliest such attacks in Egypt in years.

Analysts say the group, which surfaced in Egypt’s restive Sinai Peninsula last year, is probably responsible for most of the more complex and sophisticated operations against security compounds in Egypt since the military coup. The group has claimed responsibility for several major car bomb attacks in Egypt in recent months, including an attempt to assassinate the interior minister in a Cairo suburb in September.

In the statement released to jihadist forums Wednesday, Ansar Bayt al-Maqdis warned Egyptian police and soldiers to abandon their posts and stop working for the government “to preserve their religion and lives.”

Hours after the car bomb ravaged buildings across a wide city block in Mansoura, anti-Islamist crowds roamed the streets and burned and looted Brotherhood-linked businesses. Residents chanted slogans against the Islamists in the street, and others played pro-military songs.

Many in Egypt seemed to welcome the government’s escalation of its fight against the group. The front-page headline of the privately owned Egyptian daily, al-Youm al-Sabea, on Wednesday read: “The people want the execution of the Brotherhood.”

Ahmed Abdel Rahman Fawzi, a psychiatrist whose clinic was destroyed in the car bombing, said calls for revenge “will just bring more chaos and destruction.”

“What we need,” said Fawzi, 29, “is an independent investigation into who” perpetrated the attack.

Sharaf al-Hourani contributed to this report.