CAIRO — Egyptian security forces have expanded a crackdown on anti-government protesters, arresting hundreds, including political opponents, while restricting access to news websites and social media channels as the nation braces for possible new protests this week.

As of Monday evening, more than 370 people had been arrested since small but rare protests broke out in Cairo and other areas Friday night and Saturday, demanding the removal of Egypt’s authoritarian President Abdel Fatah al-Sissi, according to two local human rights organizations. Most face potential charges of belonging to a terrorist group, spreading fake news and joining unauthorized protests.

“The regime is trying to contain the situation,” said Mohamed Lotfy, executive director of the Egyptian Commission for Rights and Freedoms. “They are focusing their energy on preventive measures.”

The government has also arrested a prominent human rights lawyer representing some of the detained protesters, as well as two leaders of opposition political groups, rights activists said.

 In an apparent attempt to curb the use of social media to organize more protests, authorities restricted access to Facebook Messenger and some other servers, according to Netblocks, a group that monitors digital censorship. The BBC and other news websites were also restricted, the group said.

Hundreds of websites deemed critical of the government have been blocked for more than two years now.

 The crackdown comes after a former government contractor and part-time actor, Mohamed Ali, issued a new video calling for Egyptians to stage a “million-man march” this Friday. Sissi, who is attending the U.N. Climate Summit with other world leaders this week, has not publicly commented on the protests that have rattled his regime unlike any moment in his presidency.

Over the past three weeks, Egyptians have been riveted by a string of videos Ali posted online from Spain, alleging corruption by Sissi and his generals. Among Ali’s claims: that Sissi used taxpayer funds to build a luxury hotel for an army general and close friend, as well as a palace for himself and his wife. Sissi has denounced the videos as “lies and fabrications.”

Although Ali has yet to provide any concrete evidence, his allegations appear to have struck a chord with millions of Egyptians disillusioned by the country’s growing poverty, rising prices and repression. Last week, his call for protests spurred hundreds to take to the streets in 14 provinces to demand the end of Sissi’s rule.

Over the weekend, protesters in some areas clashed with security forces, who used tear gas to disperse the small crowds. Elsewhere, protesters lit flares and chanted, “Sissi must go.”

Sissi, a former army general, came to power in 2014, a year after he orchestrated a military coup against Egypt’s first democratically elected president, Mohamed Morsi. Since then, his government has jailed tens of thousands of opponents and critics, often in the name of combating terrorism. But the repression, critics say, is actually aimed at preventing a populist revolt like the one in 2011 that toppled President Hosni Mubarak — and at cementing Sissi’s grip on power.

That explains the intensity of the ongoing crackdown, according to Riccardo Fabiani, North Africa project director at the International Crisis Group.

“These protests have now pierced the ‘wall of fear’ and are a major source of concern for the regime,” he said in a tweet Monday. Ali’s calls for massive protests this Friday, he added, “is likely to be a key test for the regime and for the strength of this spontaneous movement.”

Neither side is taking any chances. In downtown Cairo and other cities, armored vehicles, plainclothes security and intelligence agents and truckloads of police are positioned in potential protest locations. Activists on social media are warning Egyptians to use encrypted applications to communicate and to clear sensitive information from their phones, in case they are confiscated.

Lotfy, the rights activist, said the arrest numbers are expected to soar.

“The regime hasn’t struck back yet,” he said. “Striking back means they will come to people’s homes and start arresting activists. There is fear, but there is also fear within the regime that next Friday, the protests will be even larger.”