Soldiers stood guard and helicopters hovered overhead as demonstrators gathered to demand President Hosni Mubarak's resignation.
Egypt's government posted troops at key locations and cut internet service as activists pledged to hold major demonstrations in Cairo, Alexandria and other cities Tuesday -- a week after rallies began calling for an end to Mubarak's nearly 30-year rule.
In Cairo, protesters set up their own checkpoints to keep weapons out of Tahrir -- or Liberation -- Square.
Inside the square, the atmosphere was peaceful.
People brought food and beverages to share. Families stood together, with parents saying they came for their children. One group chanted "Down with Mubarak," while others listened to patriotic music.
Scattered groups of demonstrators supporting Mubarak were also in the area, which has been a focal point of anti-government protests.
"No to the traitors," chanted a pro-Mubarak group as it headed toward the rally site.
Inside the square, some protesters suggested marching toward Mubarak's presidential palace.
One said, "Mubarak may have thick skin, but we have sharper nails."
The embattled president has given no indication that he plans to give up power, and the Interior Ministry said Monday that it planned to shut down mobile phone networks in preparation for Tuesday's protests. As of 11 a.m. (4 a.m. ET), some cell phone service in the country was still up and running.
Banks and schools were also closed, and there was a curfew aimed to keep people off the streets after 3 p.m. But protesters have defied previous curfew orders.
It will be "a very dramatic and perhaps even a decisive day," said Nicholas Burns, a professor of diplomacy at Harvard's Kennedy School of Government and a former U.S. undersecretary of state.
"If the military cracks down on peaceful demonstrators on the streets of Alexandria or Cairo, that will be a decisive factor," he said.
The military said Monday evening that it would not open fire on peaceful protesters.
Late Monday night, Google announced a new technology option that could help Egyptians get around restrictions on mobile phone and internet service.
The "speak-to-tweet" service allows people without an internet connection to leave a voice-mail message, which will automatically be turned into a tweet, according to a description on Google's blog.
The political turmoil has paralyzed commerce and disrupted daily life in Egypt.
State television reported Monday that the crisis has cost the country an estimated 69 billion Egyptian pounds (nearly $12 billion) and set its economy back six months.
ATM screens went dark. Gas stations ran out of fuel. Long lines snaked around bakeries and supermarkets as shops began to ration how much food customers could buy.
Men with makeshift weapons guarded neighborhoods, creating checkpoints to fill the void left when police stopped patrolling the streets.
At demonstrations last Friday, thousands of riot and plainclothes police clashed violently with protesters in a brutal crackdown.
Since then, troops from the country's powerful military have had a strong presence in the streets as largely peaceful protests continued.
"The presence of the armed forces in the Egyptian streets is for your benefit to protect your safety and peace," an unnamed military spokesman announced on state television Monday night. "Your armed forces will not use violence against this great people, who have always played a significant role in every moment of Egypt's great history."
Soldiers at Cairo's Ramses Hilton hotel were putting on newly issued flak jackets -- straight out of their boxes -- on Tuesday morning.
Troops have been mingling with demonstrators in Cairo's Tahrir Square.
"There is no aggressive behavior from the army toward the peaceful assemblies," human rights activist Ramy Raoof said early Tuesday. "We hope that within a few hours, the same also will happen. We hope the army will not escalate violence against us."
Mubarak, now 82, imposed an emergency decree after the 1981 assassination of his predecessor, Anwar Sadat. Since then he has ruled with an iron fist. The wave of protests against Mubarak's regime erupted following the uprising in Tunisia that ousted its longtime strongman January 14.
"I urge the Egyptian authorities to ensure police and other security forces scrupulously avoid excessive use of force, and there needs to be a full investigation into the role of security forces in the violence that occurred over the past few days," Pillay said in a statement.
While it was widely believed Mubarak was grooming his son, Gamal, as his successor, that plan now has been complicated by demands for democracy.
Mubarak fired his Cabinet on Saturday and his designated longtime intelligence chief Omar Suleiman as vice president -- the first time he has filled that post since he came to power in 1981.
Suleiman announced Monday that he had begun discussing reform with opposition parties. Speaking on the state television network, Suleiman said a reform package should be drawn up "expeditiously." "The other parties will also have a role to play, which will lead to real political reform," Suleiman said.
But there were no details about what proposals might be on the table or which parties were taking part.
Several opposition movements have been represented on the streets in the demonstrations.
Mounir Fakhry Abdel Nour, secretary-general of the Wafd Party, told CNN the group's followers have been "extremely active."
Raoof, the human rights activist, said that many people with different perspectives were banding together around a common goal.
"There is no political group leading the people. There is no one leading the people. People are going in a very organic way ... people are just doing it," he said.
But others said they were opposed to the protests.
"I am upset with the revolution in Tahrir Square," said Muna al-Mahdi, her voice trembling with emotion as she spoke in her middle-class Cairo neighborhood. "It doesn't represent us. It doesn't represent our opinion. We are here sticking with Hosni Mubarak only.
"Give him two months, give him time to work," she says. "And then he can go peacefully."