Operation at the Mada Masr offices comes a day after Egyptian security forces arrested one of its editors, Shady Zalat.

Egyptian news outlet Mada Masr said on Sunday security forces raided their Cairo office and arrested three other journalists before releasing them.

“Plain-clothes security forces have raided Mada Masr’s office in Cairo. Staff are currently being held inside, and their phones have been switched off,” the independent news site posted on Twitter.

Journalists Rana Mamdouh, Mohamed Hamama, and Lina Attalah were arrested and taken to Cairo’s Dokki police station, but were released a few hours later, Mada Masr said.

A plainclothes man told the rest of the staff that the three colleagues were being taken to the prosecution. When asked, he refused to designate which one. When asked to identify himself or the agency he worked for, he also refused. — Mada Masr مدى مصر (@MadaMasr) November 24, 2019

The raid comes after Shady Zalat, 37, a news editor who has worked since 2014 at the prominent website, was arrested at his home on Saturday.

Mada Masr also said lawyer Mahmoud Osman was prevented by security forces from entering the office.

The Committee to Protect Journalists (CPJ) issued a statement condemning the raid and arrests, calling on Egyptian authorities to end their “retaliation campaign” against Mada Masr.

“Mada has shown nothing but courage in reporting the news against all odds and in the face of brutal repression,” said Sherif Mansour, CPJ’s Middle East and North Africa Program Coordinator.

Among the journalists now locked inside are: @Linaattalah, co-founder, quadrilingual polymath, regularly named among the most influential people in the region.@Sharifkouddous, news editor, major international journalist, Democracy Now correspondent, Emmy winner. — Omar Hamilton (@ORHamilton) November 24, 2019

Mada Masr publishes investigations into corruption and security issues in Arabic and English.

It published an explosive article last week alleging that President Abdel Fattah el-Sisi‘s son Mahmoud had been transferred to Moscow on a diplomatic posting.

His reassignment from a senior intelligence post came after he had been criticised internally within the security apparatus, Mada Masr reported.

The article, which cited unnamed Emirati and Egyptian officials, gave details about the country’s security agencies at a time when press freedom in Egypt is shrinking.

The @MadaMasr office was raided. My heart sank reading the news. They're a pillar of exemplary journalism facing off with authoritarianism. No one working on Egypt doesn't rely on them. This latest report is likely what the govt doesn't want you to read https://t.co/DQipn9QqCE — Timothy E Kaldas (@tekaldas) November 24, 2019

A journalist from Mada Masr, speaking from outside the news site’s building, told AFP news agency on Sunday that police officers were still inside.

He described seeing several vehicles belonging to security forces and was met by plain-clothes officers at the entrance of the building.

“They initially prevented me from entering then they took me up to the sixth floor where the office is. We knocked on the door and I saw my colleagues for a fraction of a second,” he said.

“A policeman, also plain-clothed, said ‘we don’t want anyone coming or going’ and I was let go,” he added.

A police spokesman was not immediately available for comment.

Egypt jails more journalists than any other country behind China and Turkey, according to the New York-based watchdog Committee to Protect Journalists.

Mada Masr is one of the hundreds of websites blocked by Egyptian authorities in recent years and can only be accessed domestically via a virtual private network (VPN) application.

Al Jazeera journalist Mahmoud Hussein has been imprisoned without any formal charges in Egypt for 1,066 days.

Hussein, an Egyptian national who works for the Al Jazeera Arabic television channel in Qatar, was arrested on arrival in Egypt on December 20, 2016, while on a personal visit to see his family.

Several other Al Jazeera journalists have also been charged in absentia, accused of spreading lies and supporting “terrorists” – a reference to the outlawed Muslim Brotherhood organisation.