The Chancellor raised Deniz Yücel’s case with Turkish Prime Minister Binali Yildirim on the sidelines of an international conference in Munich, her spokesman said.
“She pointed out the importance of the German Embassy being given unrestricted consular access to Mr Yücel,” Steffen Seibert told Reuters.
“The Chancellor expressed the federal government’s expectation that Deniz Yücel will be treated fairly and in accordance with the law.”
The Turkey correspondent for Die Welt has been in custody for five days after reporting on a minister’s hacked emails concerning media control and the use of fake Twitter accounts to influence the public in favour of the ruling AKP party.
Mr Yücel has been accused of being a member of a terrorist organisation, spreading “terrorist propaganda” and misusing information for reporting on the cache of almost 58,000 emails dating back 17 years.
Redhack, a Turkish activist group, allowed Wikileaks to publish Berat Albayrak’s emails after the Turkish government refused its demands to release imprisoned opposition politicians and activists, and then blocked access to its sites.
Mr Albayrak, a prominent businessman before entering politics, is the Turkish President’s son-in-law and was made energy minister just five months after being elected to parliament in 2015.
He has denied alleged links with a company suspected of smuggling Isis oil into Turkey, while the leaked emails include discussions over plans made by Recep Tayyip Erdogan’s officials to employ pro-AKP trolls to influence Twitter during mass protests in 2013.
Hacked emails also appear to show Mr Albayrak lobbying to keep one of Turkey’s largest media group’s under the control of the government or an allied business, rather than returning it to its owners.
Mr Yücel, who holds both German and Turkish citizenship, visited a police station in Istanbul to answer investigators’ questions over the hack on Tuesday and was taken into custody.
The 43-year-old’s apartment was searched, Die Welt said he was one of at least seven other journalists arrested in connection with the emails, of whom three have been accused of belonging to different “terrorist” groups.
Under expanded powers allowed by Turkey’s ongoing state of emergency, he can be held in police custody for up to 14 days without a hearing before a judge.
“Our correspondent Deniz Yücel does excellent work,” said the newspaper’s editor-in-chief, Ulf Poschardt.
“The Turkish government constantly stresses that Turkey is beholden to the rule of law. Therefore we trust that fair proceedings will prove his innocence.”
In pictures: Turkey coup attempt
In pictures: Turkey coup attempt
Turkish President Erdogan attends the funeral service for victims of the thwarted coup in Istanbul at Fatih mosque on July 17, 2016 in Istanbul, Turkey
Burak Kara/Getty Images
Soldiers involved in the coup attempt surrender on Bosphorus bridge with their hands raised in Istanbul on 16 July, 2016
A civilian beats a soldier after troops involved in the coup surrendered on the Bosphorus Bridge in Istanbul, Turkey, 16 July, 2016
Surrendered Turkish soldiers who were involved in the coup are beaten by a civilian
Soliders involved in the coup attempt surrender on Bosphorus bridge
Supporters of Turkish President Recep Tayyip Erdogan wave flags as they capture a Turkish Army vehicle
People pose near a tank after troops involved in the coup surrendered on the Bosphorus Bridge in Istanbul, Turkey, 16 July, 2016
Turkish soldiers block Istanbul's Bosphorus Brigde
A Turkish military stands guard near the Taksim Square in Istanbul
Turkish soldiers secure the area as supporters of Recep Tayyip Erdogan protest in Istanbul's Taksim square
Turkish soldiers detain police officers during a security shutdown of the Bosphorus Bridge
Turkish Army armoured personnel carriers in the main streets of Istanbul
Chaos reigned in Istanbul as tanks drove through the streets
Turkish President Tayyip Erdogan speaks to media in the resort town of Marmaris
Supporters of President Erdogan celebrate in Ankara following the suppression of the attempted coup
Germany’s foreign ministry said it was doing everything it could to support him, with a statement adding: “We hope the ongoing investigation by Turkish authorities against Mr Yücel respects the rule of law and he is treated fairly, in particular with regard to the press freedom that’s guaranteed by the Turkish constitution.”
The incident threatened to worsen relations between Germany and Turkey, which have been damaged by ongoing tensions over Ankara’s attempt to join the EU and gain visa-free travel in the Schengen zone.
But Mr Erdogan has refused to make required reforms to human rights protections, prompting a European Parliament vote to pause membership talks, and threatened to allow thousands of refugees into Europe by scrapping the EU-Turkey deal.
According to the Committee to Protect Journalists, a press freedom group based in New York, at least 81 journalists were imprisoned in Turkey last year – the biggest number worldwide.
Many of the arrests came after July’s coup attempt, which prompted a government crackdown on alleged anti-government activists that included the closure of at least 100 news outlets and mass purges in politics, the military, civil service and judiciary.
Mr Erdogan accuses the Hizmet movement run by US-based cleric Fethullah Gülen of fomenting the coup, although it denies the allegations and American authorities have refused to deport the Turkish preacher.
Critics accuse the Turkish government of using terror allegations and false links to Hizmet in attempts to silence all dissent, with the crackdown prompting warnings from the United Nations.