Family and friends of a British-Syrian journalist arrested in Turkey have expressed concerns at his safety after it emerged he is being detained with Islamist State (Isis) militants. Rami Jarrah, 31, was held on 16 February as he applied for a residence permit in the southern Turkish city of Gaziantep.

Colleagues at the citizen journalist group he co-founded, ANA Press, said they managed to get in touch with him after three days with no information and found out he had been moved to a prison 200km to the west in the city of Adana.

"[He is] imprisoned with a number of Isis elements," they said. "He also added to have argued with one of them and that he feels not to be safe being imprisoned with them."

An independent reporter, Jarrah, became known in the early stages of the Syrian revolution for his work under the pseudonym of Alexander Page and has in recent years covered all aspects of the conflict, including atrocities committed by IS (Daesh).

Reasons for his arrest were not clear. ANA press co-director Deiaa Dughmoch said he feared Jarrah might have been mistaken for an IS member. He pointed to unconfirmed rumours that intelligence passed on by Russia to European agencies and then to Turkey falsely identified some pro-democracy Syrian opposition members as jihadists. The EU crime agency, Europol, has denied sharing part of its database on foreign fighters and Islamist suspects with Turkey.

After Jarrah was arrested, immigration authorities repeatedly refused to provide his lawyer with any information, Dughmoch told IBTimes UK. An immigration official used the expression "Ankara wants him", to suggest the reporter had been detained on the orders of the central government but did not elaborate, he said.

Jarrah's father, Nouri, said he was "surprised and concerned" at his son's imprisonment. "I demand his immediate release," he wrote in an online statement. "I hold the Turkish authorities fully responsible for his safety".

The 31-year-old had recently been covering the Russian bombing campaign in northern Syria as well as the IS and the resurgence of the Assad regime. Colleagues said he returned to Turkey from Syria a few weeks ago.

Ironically, at the end of January, he was part of a delegation of reporters that met with Turkish President Recep Tayyip Erdogan to discuss issues faced by Syrian reporters covering the conflict from across the border.

In December, Jarrah had posted online photos of Dughmoch's bruised face saying he had been beaten up by Turkish troops after crossing into the country following an assignment in Syria.

"President Erdogan highlighted his support for the Syrian journalists during the meeting and promised that the Turkish authorities to help their work," said Nouri Nouri Jarrah

After the summit Jarrah published on Facebook a selfie with Erdogan that drew a series of death threats from sympathisers of the Assad regime. The reporter decided to remain in Istanbul for some time over security concerns and returned to Gaziantep only earlier this week, according to Dughmoch. He was held shortly afterwards.

The Committee to Protect Journalists (CPJ) has called for his release, which is supported by an online petition that has amassed more than 5,000 signatures within a few hours.