CAIRO – Egyptian authorities installed an interim president and ordered the arrests of senior leaders of the Muslim Brotherhood on Thursday, hours after the nation’s all-powerful military ousted Mohammed Morsi, the country’s first democratically elected leader.

The Egyptian armed forces were quick to put a civilian face on what their opponents have labeled a coup. But the swift moves against the military’s longtime nemesis, the Morsi-allied Brotherhood, suggest that the nation’s generals are in no mood to reconcile with an Islamist group that until Wednesday had effectively controlled Egypt’s highest office for a year.

Authorities operating under the military’s protection swept up Morsi associates in a flurry of arrests and warrants, placing the Brotherhood even further on the defensive.

Brotherhood-allied leaders responded by calling for a “day of resistance” Friday, with nationwide protests planned after the traditional midday prayers. Although organizers called on supporters to remain peaceful, such rallies in the past have led to deadly clashes, and residents of Cairo and other areas braced for more chaos.

Egypt’s new president, a virtual unknown named Adly Mansour, vowed to include all sections of society, including Islamists, in an interim coalition government shortly after he was sworn in Thursday. But even as he spoke, an arrest warrant was issued for Mohammed Badie, the Muslim Brotherhood’s “supreme guide.”

An arrest warrant also was issued for Khairat al-Shater, a wealthy businessman who serves as Badie’s deputy and was widely seen as one of the real powers behind the Morsi presidency.

Morsi and his top aides were placed under house arrest at a military residence. At least three other Brotherhood officials were taken into custody.

In a statement late Wednesday, President Obama had urged the Egyptian military “to avoid any arbitrary arrests of President Morsi and his supporters.” But with the crackdown against the Brotherhood under way and with several pro-Islamist media outlets shuttered, many Egyptians feared a new cycle of retribution and repression.

The moves against Morsi and his closest allies represent a dramatic fall for the Muslim Brotherhood, which spent more than 80 years in brutally repressed opposition under successive Egyptian military autocrats, only to see their hold on the presidency end after 368 days.

Morsi’s ouster cheered millions of Egyptians who had grown frustrated with his failure to address the country’s debilitating economic woes and his apparent efforts to consolidate power for the Muslim Brotherhood. Mass demonstrations in recent days helped precipitate the military’s move to remove him from office.

Morsi’s Brotherhood backers must now decide how to respond. The group is vastly outgunned by the military, one of the most powerful in the Middle East. But acquiescing to the military could leave the organization looking weak and defeated.

So far, Brotherhood leaders have signaled defiance.

Murad Ali, a spokesman for the Brotherhood’s Freedom and Justice Party, said the military’s action represented “a dictatorship, and we are not accepting it.”

Prosecutors accused Brotherhood leaders of ordering 250 of their members to defend the group’s headquarters in Cairo with lethal force — specifically, to shoot birdshot and bullets at anyone who tried to storm the building. The group said days before the clashes occurred that it had been compelled to hire private security firms to guard the headquarters after police failed to protect it.

Scores of Morsi opponents attacked the building and set it on fire Sunday, part of a weekend of massive anti-government demonstrations. Eight people died in the ensuing clashes. A day later, the military gave Morsi 48 hours to forge a deal with the protesters and said it would intervene if the situation was not resolved.

On Wednesday evening, Morsi was forced from power. Gen. Abdel Fatah al-Sissi, head of the armed forces, told the nation in a televised address that the military was responding to the people’s demands in an act of “public service.”

Mansour, the 67-year-old jurist tapped to be president, told reporters that he would seek to include all elements of society in an interim coalition.

“The Brotherhood are part of the people, and they are invited to take part in building the country,” he said. “There will be no exclusion for anyone.”

Mansour also pledged to uphold the constitution, but the meaning of that promise was unclear: A constitution ratified under Morsi, which rights groups and opposition activists criticized as failing to protect the rights of women and minorities, was suspended by the army Wednesday night.

The arrests of prominent Islamists deepens the quandary facing the Obama administration, which has refrained from criticizing Egypt’s military for overthrowing a democratically elected president.

Obama met with his national security team in the Situation Room to discuss Egypt, and top U.S. officials called Egyptian and other officials in the region to stress the importance of quickly returning full authority to a freely elected civilian government and avoiding violence, the White House said. An administration official said the White House also pressed for assurances that U.S. personnel in Egypt would be protected.

Administration officials have avoided referring to the crisis as a coup, a finding that would require the U.S. government to cut off financial aid to the country.