The relatives of two German citizens detained in Egypt over alleged links to Isis deny that they have any extremist sympathies, as one was deported and the other remains in prison.

On Friday, dual German-Egyptian citizen Mahmoud Abdel Aziz was deported for “attempting to join terrorist Isis groups in Sinai”, where the army has been trying to put down an armed insurgency.

Another dual citizen, Issa al-Sabagh, remains in detention on similar accusations, having been arrested on 17 December.

An Egyptian security source, who requested anonymity, told The Independent that Abdel Aziz was deported to Germany as “so far he didn’t commit any crimes and has given up his Egyptian nationality”.

“The mentioned individual established contact with an Isis member and attempted to join the group,” the source said, adding that the deportation was coordinated by officials from the German embassy.

The embassy in Cairo is yet to release a statement.

The 23-year-old student was detained upon arrival in Cairo from Saudi Arabia on 27 December, his family told The Independent.

Mahmoud’s brother Malik denied the accusations his brother had any “fundamentalist or political affiliations”. Both brothers are students at the Islamic Studies University at Saudi Arabia’s Medina.

“We entered the country with our German passports and were headed to visit our grandparents but were held at the passport section for three to four hours,” Malik told The Independent, adding that officials later released him and informed him that Mahmoud would not be allowed to enter Egypt and would be sent back to Saudi Arabia. But he has not heard from his brother since.

In a separate incident, another young man, Issa al-Sabagh, an 18-year-old high school student from Giessen in Germany, arrived in Luxor on 17 December and was taken into custody.

Fabricating the evidence to show my son is a terrorist is an immoral act Mohamed al-Sabagh, father of deported German-Egyptian citizen

He is currently detained pending investigation on accusations of also attempting to “join Isis groups in North Sinai”.

The privately owned Egyptian news website Sada Al-Balad, which is known for its close connections to the police apparatus, reported that al-Sabagh had “maps of North Sinai and a compass”. The authorities have yet to produce any evidence for their claims, in either case.

But al-Sabagh’s father Mohamed denied that his son ever wanted to join a militant group and says he was in the country to visit family.

“Fabricating the evidence to show my son is a terrorist is an immoral act,” he said.

However he expressed relief to even find out that his son was alive, almost a month after he went missing.

“He is just a kid. He knows nothing about politics, but I am glad that he is alive. Ever since he was detained, we have been thinking of that Italian student who they kidnapped and was later found dead,” the father told The Independent, speaking from Germany.

Italian student Giulio Regeni disappeared in Cairo in January 2016. His body was discovered more than a week later. He had been tortured to death.

The Italian government has accused members of Egypt’s National Security Agency of being behind Regeni’s killing, a narrative rejected by Cairo, which claimed a gang targeting foreigners had killed the Cambridge University student.

“Issa wanted to visit Cairo on his own as well as visit his 93-year-old grandfather,” he said adding that he grew concerned when he tried to call his son after his flight was due to land, and Issa did not answer his phone.

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“I kept calling him and someone picked up the phone but no one said anything. Then I contacted EgyptAir, and they told me that he checked in but didn’t board the plane to Cairo. I knew then that something was wrong,” the father added.

Several Egyptian media outlets have published mugshots and the passport images of both young men, and video footage of Abdel Aziz at the Lufthansa Airlines desk.

Al-Sabagh’s father told The Independent that his son had gone to Egypt for a two-week vacation in Cairo. Issa opted to book a cheaper ticket that would land in Luxor instead of Cairo, the father said.

“We often hear about families breaking down when their sons are in detention, but I never thought I would be put in this situation,” he said.

Egyptian president Abdel Fattah el-Sisi denies his country holds political prisoners

On Monday, Christofer Burger, the German foreign ministry spokesman, said that his country is “taking both cases very seriously”.

Rights groups in Egypt claim that the tactic of enforced disappearances has become an unofficial security policy of President Abdel Fattah al-Sisi’s military government in response to economic instability and an Islamist insurgency in the Sinai.

In the five years since Sisi came to power in a military coup, Egyptian security forces have arrested or charged at least 60,000 people, according to Human Rights Watch. Torture of political detainees has become widespread and endemic, and no opposition to the government is tolerated, it says.