Turkish authorities have arrested a reporter for a prominent German newspaper on charges of propaganda in support of a terrorist organisation and inciting the public to violence, according to a court witness.

Authorities initially detained Deniz Yücel, a correspondent for Die Welt newspaper, on 14 February after he reported on emails that a leftist hacker collective had purportedly obtained from the private account of Berat Albayrak, Turkey’s energy minister and the son-in-law of Turkey’s president Recep Tayyip Erdoğan.

On Monday, an Istanbul court ordered Yücel, a dual citizen of Turkey and Germany, to be jailed pending trial, a witness at the court told Reuters. He is the first German reporter to be held in a widespread crackdown that has followed last year’s failed 15 July coup in Turkey and has frequently targeted the media.

More than 100,000 people have been sacked or suspended from Turkey’s police, military, civil service and private sector since the failed coup and tens of thousands arrested. Ankara says the measures are necessary given the security threats it faces.

But Turkey’s allies, including Germany, fear Erdoğan is using the purges as a pretext to curtail dissent. Relations between the Nato allies have been strained by the coup but Germany desperately needs Turkey for its part in a deal to control the flow of migrants into Europe.

Yücel’s arrest could also put the German chancellor, Angela Merkel, into an awkward position less than seven months before what promises to be a tightly contested election in September. Merkel criticised the move as “bitter and disappointing” and called it “disproportionate”.

She said: “The German government expects that the Turkish judiciary, in its treatment of the Yücel case, takes account of the high value of freedom of the press for every democratic society. We will continue to insist on a fair and legal treatment of Deniz Yücel and hope that he will soon regain his freedom.”

Germany’s foreign minister, Sigmar Gabriel, was even more harsh in his assessment of the case, saying it showed in “glaring light” the differences in the two countries in evaluating freedom of press and freedom of opinion.