CAIRO — Egyptian security agents stormed the offices of an outspoken online publication and detained its staff for several hours Sunday, a day after one of its editors was arrested, the media site said.

The targeting of Mada Masr, one of the few remaining independent media organizations in the country, was another sharp blow to press and personal freedoms in Egypt.

Nine plainclothes security agents entered the publication’s downtown Cairo premises at 1:30 p.m. Sunday and immediately confiscated laptops and phones, the media site said on Twitter. The journalists were not permitted to leave the newsroom, according to the site, and their attorney was not allowed to visit them.

The security agents later briefly arrested the site’s top editor and two journalists.

 The journalists in the newsroom included at least one American citizen and two Europeans. A French television crew there to film a story was also caught in the sweep.

Early Saturday, four plainclothes security officers arrested Shady Zalat, an editor at Mada Masr, after entering his home without presenting an arrest warrant, the media site said. The agents confiscated the laptops of Zalat and his wife, work documents and his cellphone before taking him to an unknown location.

Zalat was released Sunday evening. The media site said security forces dropped him off beside a busy highway that encircles Cairo.

Mada Masr was the latest target in a widening crackdown by the government of President Abdel Fatah al-Sissi. Since Sept. 20, when small but rare street protests flared up against Sissi, the government has arrested more than 4,400 people, including activists, political opponents, even children and some foreigners, according to human rights activists.

The Committee to Protect Journalists ranked Egypt this year among the world’s top jailers of journalists. The Sissi government has blocked hundreds of websites, including Mada Masr, viewed as too outspoken or critical of the regime.

At least eight journalists have been arrested since the September protests, CPJ said.

Mada Masr is widely seen in Egypt and across the Arab world as among the most reputable news organizations, unafraid to investigate sensitive subjects such as corruption, human rights or the internal workings of the Egyptian state.

“Mada has shown nothing but courage in reporting the news against all odds and in the face of brutal repression,” Sherif Mansour, CPJ’s program coordinator for the Middle East and North Africa, said in a statement denouncing Sunday’s raid.

It’s unclear what prompted the raid. Mada Masr reported last week that Mahmoud al-Sissi, one of the president’s sons, had been removed from a senior position in the intelligence services and dispatched to a diplomatic job in Moscow. It was seen as a demotion and a blow to his father’s efforts to bolster his son’s influence.

“Egypt’s last remaining independent news outlet was apparently too much for President [Sissi],” tweeted Kenneth Roth, executive director of Human Rights Watch. “Its most recent scoop: showing how [Sissi’s] efforts to build a dynasty were thwarted, with his son sent to Moscow.”

Egyptian authorities could not be reached for comment. They have publicly said that those arrested since September were influenced by fake social media posts and forces plotting against Egypt.

The security agents Sunday appeared to be looking for evidence to use against Mada Masr, the media site said. They confiscated journalists’ identification cards and ordered some to unlock their phones and laptops.

Lina Attalah, the site’s top editor, and other staffers were questioned by the agents over several hours. Also questioned were the television crew members from France 24. They later left with French Embassy representatives.

By late afternoon, all the journalists were allowed to leave. But Attalah and two other staffers were taken to a police station in the Cairo enclave of Dokki, the news site reported. All three were later released.