Egyptian security forces completely sealed off Tahrir Square, the epicenter of the so-called Arab Spring uprising in 2011, to prevent possible protests on Friday against the country's president.
The closures come amid a harsh security clampdown following rare demonstrations in several cities last weekend, all of which were broken up by police.
Lawyers say over 2,000 people have been arrested since then. Egypt's general prosecutor claims his office has questioned no more than 1,000 people over the latest protests.
Street demonstrations have been almost completely silenced the past years by draconian measures imposed under President Abdel Fattah el-Sissi, a former general.
The weekend demonstrations erupted over corruption allegations levelled earlier this month against the military and el-Sissi.
Those allegations were made by an Egyptian businessman living in self-imposed exile who said he had worked with the military for 15 years.
El-Sissi warned Friday against "deceitful" attempts to discredit his rule.
Riot police barricaded streets and bridges leading into Tahrir Square, where hundreds of thousands had gathered in 2011 to demand the ouster of longtime ruler Hosni Mubarak.
Several subway stations in the downtown area were closed for alleged maintenance.
The government effectively banned all public protests in 2013, shortly after el-Sissi led the military's overthrow of an elected but divisive Islamist president, amid mass protests against that president's brief rule.
Earlier this month, Mohamed Ali, the self-exiled contractor, posted inflammatory videos accusing the president and some military commanders of misuse of public funds to build presidential palaces and a tomb for the president's mother.
The allegations came as economic reforms and austerity have squeezed Egypt's lower and middle classes badly.
Ali has renewed his call for Egyptians to take to the streets Friday, the first day of the weekend.
El-Sissi arrived Friday morning to Cairo from New York, where he had been attending the UN General Assembly at the time the protests broke out.
"It is all based on lies, distortion and fabrication. You should be aware of that," el-Sissi said upon his arrival at Cairo airport.
Hundreds of his supporters rallied to greet him, raising his picture and waving Egyptian flags.
Human Rights Watch said Friday that Egypt's authorities should respect the right of peaceful assembly by allowing protests, and should release all those arrested.
"The nationwide crackdown on protests suggests that President Abdel-Fattah El-Sissi is terrified of Egyptians' criticisms," said Sarah Leah Whitson, the group's Middle East and North Africa director.
Since Ali posted his first video, state-run media have responded with a staunch campaign linking him to the outlawed Muslim Brotherhood group and accusing him of instigating chaos.
"They won't let you achieve any success or enjoy anything; we are at war with them," said el-Sissi, an allusion to the Muslim Brotherhood.
The group was banned after the 2013 overthrown of late president Mohamed Morsi, who hailed from the group.
Since then, the group's members were either jailed or forced into exile.
Pro-government protests were scheduled later in the day in east Cairo.
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