The commander of the armed forces asked Egyptians on Wednesday to hold mass demonstrations that would give him a "mandate" to confront violence and terrorism, appealing to one side of Egypt's sharply divided populace and raising the specter of broader unrest.
During a speech to recent military graduates, the commander, Gen. Abdul-Fattah el-Sisi, warned of forces taking the country into a "dark tunnel," a clear reference to Islamist supporters of the deposed president, Mohamed Morsi, and he asked Egyptians to protest on Friday.
"I'm asking you to show the world," he said. "If violence is sought, or terrorism is sought, the military and the police are authorized to confront this."
The call for mass mobilization thrust the general into the center of Egypt's contentious politics, raising questions about his ambitions while contradicting the military's pledges to defer to civilian leaders after removing Mr. Morsi. His appeal also hinted at a broader crackdown against Islamists, whose leaders have already been detained.
As the Muslim Brotherhood planned competing protests on Friday, Egyptians faced another threat of bloody street clashes in what has become a long and wearying cycle.
In a statement, the Brotherhood said the general's speech amounted to a call for "civil war."
Michael Wahid Hanna, who studies Egyptian politics at the Century Foundation, a left-leaning policy group, said the speech was "pretty ominous."
"At best this was an irresponsible effort to isolate the Muslim Brotherhood, to gain leverage in whatever negotiations ensue," he said. "At worst, it will green-light violence at lower levels and potentially provide a mandate to use force to break up the sit-in," a reference to the Cairo encampment of Mr. Morsi's supporters.
"Neither of those things is good," Mr. Hanna added.
Wednesday's developments cemented a standoff between the Brotherhood and the military that started after the generals removed Mr. Morsi from power on July 3. Since then, the military has held Mr. Morsi incommunicado in an undisclosed location, ignoring calls from Western allies and the United Nations to release him. An interim government has pressed ahead quickly, securing financial aid and beginning the process of amending the Constitution, while trying to fend off questions about its own legitimacy.
The Brotherhood has adopted an increasingly confrontational stance to support its effort to restore Mr. Morsi to power. The group's sit-ins have given way to daily marches, many of which have been attacked by shadowy armed groups. Other marches are clearly intended to provoke a response.
While General Sisi's speech intensified Islamist fears about the return of a police state, it may well have strengthened the Brotherhood's hand.
"The Brotherhood needs the repression to get worse, to effectively make their case to the broader public," said Shadi Hamid, a researcher at the Brookings Doha Center in Qatar who studies the group.
Brotherhood leaders quickly seized on the speech as evidence that General Sisi was Egypt's new dictator, saying that the country had returned to "fascist military rule that confiscates the people's freedom, sovereignty and dignity."
"We hold General Sisi completely responsible for any blood that is shed from any Egyptian citizen, as well as for deepening national division," the group said.
The arguments between the Islamists and the military, as well as General Sisi's turn in the spotlight, further sidelined Egypt's civilian government, which was mostly silent on Wednesday.
A conference on Wednesday that the government billed as an effort at national reconciliation was overshadowed by the speech. It was also boycotted by the very Islamist forces, including the Brotherhood, whose grievances have widened Egypt's divide.
Neither the interim president nor the prime minister spoke publicly about the general's call for mass protests. On Wednesday evening, a spokesman for the president was quoted in the state newspaper praising the military.
"Egypt started the war on terrorism, and the call of General el-Sisi is to protect the revolution and the state," said the spokesman, Ahmed Al-Muslimani.
Hours before General Sisi's speech, unidentified attackers bombed a police station north of Cairo, raising the specter of a new kind of political violence.
Speaking to the military graduates in the coastal city of Alexandria, General Sisi warned Egyptians and the country's "political forces" of the need to confront such violence.
"We aren't going to wait until there's a big problem and then ask, 'Why did this happen?'" he said.
The speech, by turns paternal and confrontational, was largely devoted to rebutting criticism that the general had betrayed Mr. Morsi, who promoted him nearly a year ago. General Sisi also insisted that the promised transition to an elected government would not be derailed.
"Please never think it could be abandoned, even for a moment," he said.