Egypt has extended the detention of a journalist accused of “releasing false news aimed at spreading terror” and “joining a banned group” by 15 days pending further investigation, a rights group has said.

The Egyptian Center for Economic and Social Rights (ECESR) called on Egyptian authorities to release the award-winning investigative journalist, Ismail Alexandrani, with immediate effect and without condition.

In a statement released late on Tuesday signed by 12 rights groups, the ECESR said: “They [Egyptian authorities] decided to keep him in detention for another 15 days while he is under investigation,” adding that there were three charges against him.

The first is “joining an illegal group”, the second is “promoting the group despite knowledge of what it called for”, and the third charge was “releasing false news aimed at spreading terror”.

Alexandrani denies all the charges.

His detention, the group said, “is in clear violation to his freedom”, adding that officials had searched the journalist’s mobile phone and laptop.

Held at Hurghada

Alexandrani, 32, was first held at 1pm on Sunday as he flew into Hurghada airport from Berlin, when his passport was confiscated.

On Tuesday, the third day of his detention, he was questioned in New Cairo for more than eight hours from 10am local time, said his wife Khadeega Gafar on Tuesday, speaking to Al Jazeera by phone from the Egyptian capital.

While waiting outside the Homeland Security’s headquarters for news, she said that Alexandrani’s lawyers joined him at 12.30pm.

“I am overwhelmed by all of what’s going on,” she said. “I am stressed.”

Later on Tuesday, she said she was allowed to see her husband of three years for the first time since Sunday, and that he was in good health.

Joe Stork, Human Rights Watch deputy Middle East director, said: “The arrest of Ismail [Alexandrani] is deeply disturbing and fits a pattern of Egyptian security agencies arresting people whose writings don’t conform to official views.”

According to the Committee to Protect Journalists, as of June, 18 journalists were imprisoned in Egypt in relation to their work, the highest number since the group began keeping records in 1990.

‘Paranoia about nationalism’

Alexandrani had participated in a conference on counterterrorism in Berlin recently.

“He was returning to Egypt after some time away to see his family. It was his plan to fly via Hurghada, not Cairo, to avoid interrogation,” she added.

Since 2013, Egyptian authorities have cracked down on freedom of expression after the ouster of democratically elected President Mohamed Morsi of the Muslim Brotherhood.

“Some members of the Muslim Brotherhood attended [the Berlin conference], but Ismail is critical of the Muslim Brotherhood,” she said.

“The security services know this. He’s criticised them [the Muslim Brotherhood] on social media. He is anti-Muslim Brotherhood,” she added. “They [Egyptian authorities] are just very sensitive … if you are in the same place as people from the Muslim Brotherhood, then this is a problem for them.”

According to his Twitter profile, Alexandrani is also an “expert in Sinai and Egypt’s extremities, Islamism and post-Islamism, and a human rights activist”. He was also a visiting fellow at the Washington DC-based Woodrow Wilson International Center for Scholars.

In 2014, he won the Open Eye-Hany Darweesh Award for an exceptional essay, and a prize from the World Youth Movement for Democracy in 2009.

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Angelita Baeyens, programmes director at the Robert F Kennedy Human Rights organisation in Washington DC, told Al Jazeera that Egypt’s crackdown on free speech is of “deep concern”.

“Although the charges against Alexandrani, if any, and the particular circumstances of his detention have not yet been made clear,” she said, “the ongoing harassment of activists, independent journalists, and human rights defenders in Egypt remains a deep concern and raises serious questions about the country’s commitment to respecting the rights of its citizens to freedom of expression and association.”

According to HRW, more than 3,700 civilians have been charged in military courts since October 2014, when President Abdel Fattah el-Sisi expanded the jurisdiction of military courts for a two-year period.

Many of those civilians were charged in the military courts “for acts related to protesting and [alleged affiliation with] the Muslim Brotherhood”.

The detention is part of a wider “paranoia about nationalism,” said Gafar. “[Authorities worry] that maybe you are saying something not in favour of the regime. They make Egypt and the regime the same, and accuse that you are not patriotic enough.”

Follow Anealla Safdar on Twitter: @anealla