On Wednesday afternoon, the Interior Ministry said in a statement that it was determined to maintain order. "The police force stands side by side with the armed forces in protecting the country and the citizens," it said.
Reports of a TV studio takeover
Reuters and several other news organizations reported that Egyptian troops had "secured the central Cairo studios of state television" as the deadline approached and that staff not working on live shows had departed.
CNN has not confirmed the reports; state television denied in an on-air banner that there was any additional military presence at its studios.
Massive demonstrations for and against the former Muslim Brotherhood leader who was elected to office a year ago have been largely peaceful.
But 23 people died, health officials said, and hundreds more were injured in clashes overnight at Cairo University, the state-funded Al-Ahram news agency reported.
Protest leaders have called for nonviolence.
Egypt's military met Wednesday with religious, national, political and youth leaders to address the crisis, Egyptian military spokesman Ahmed Ali said through his Facebook page.
Hours earlier, an opposition spokesman accused the United States of propping up Morsy out of concern for neighboring Israel.
"The hour of victory is coming," said Mahmoud Badr of the Tamarod opposition group. He predicted that the "illegitimate president" would be gone by the end of the day.
"Not America, not Morsy, not anyone can impose their will on the Egyptian people," Badr said.
With the ultimatum, the armed forces appeared to have thrown their weight behind those opposed to Morsy's Islamic government.
Early Wednesday, soldiers and police set up a perimeter around the opposition's central meeting point, Cairo's Tahrir Square, "to secure it from any possible attack," the state-run EgyNews agency reported.
It was the police who, on the same spot in 2011, killed hundreds when they fired upon democratic, moderate and Islamic demonstrators seeking to overthrow Hosni Mubarak, the country's longtime autocratic leader and U.S. ally.
Mubarak had long repressed the Muslim Brotherhood, an Islamic political movement that emerged as the nation's most powerful political force once Mubarak was ousted.
Many of the democratic reformers and moderates who accused Morsy's government of moving in an authoritarian direction now support former Mubarak allies and others fed up with the nation's direction in calling for the restoration of order through the military.
They are pushing to oust Morsy and his Muslim conservative government, whose leaders were drawn primarily from the ranks of the Muslim Brotherhood. They say they have collected more than 20 million signatures on a petition to remove him -- millions more than the number who voted Morsy into the presidency.
In recent days, anti-Morsy demonstrators have ransacked Muslim Brotherhood offices all over the country.
Brotherhood members have complained that police did not protect them. Some have taken matters into their own hands, in one instance firing upon vandals with shotguns, an international journalism association reported.