Chancellor Angela Merkel expressed concern Tuesday about a German journalist working for a public broadcaster being denied entry to Turkey.
Volker Schwenk, who reported extensively in Libya during the Arab Spring and now heads broadcaster ARD's regional TV team in Cairo, had planned to report on a story about refugees in the Syrian border region.
"Last stop Istanbul. Refused entry to Turkey. [Apparently] there was a comment attached to my name. Am a journalist. A problem?" Schwenk tweeted early Tuesday.
After being held for nearly 12 hours at the airport, he was allowed to fly back to Cairo.
The German government views the incident "nationally with some concern," Merkel told a press conference in Berlin.
She said the German Foreign Ministry was seeking to ensure that Schwenk could quickly resume his work.
Public broadcasters SWR and ARD said they were in contact with the Foreign Ministry and the German embassy in Ankara throughout the incident.
On ARD's evening news broadcast, Schwenk said his still did not know "the exact reason" why he was denied entry. Colleagues in Istanbul had learned it was "something to do with border violations," he said.
Schwenk said he was well-treated by Turkish police and allowed free movement inside a police station, but not allowed to leave the premises.
The Foreign Ministry in Berlin would not confirm Schwenk's identity but said it was aware a German citizen had been denied entry to Turkey and that consulate staff had gone to the airport to make contact with him.
Schwenk has gone on several reporting trips to rebel-held areas in northern Syria. Like many journalists, he chose to travel via Turkey.
Ankara had long tolerated this practice but recently toughened its stance, saying such movements constitute illegal border crossing.
Ankara and Berlin are engaged in a diplomatic stand-off that resulted last week in Merkel authorizing criminal proceedings against a German TV comedian who insulted Turkish President Recep Tayyip Erdogan.
German Vice Chancellor Sigmar Gabriel criticized the actions during his visit to Morocco on Tuesday, calling it "more than problematic that [Schwenk] doesn't have free movement within Turkey" and saying that journalists and reporters can't be treated that way.
In March, Hasnain Kazim, a reporter for news magazine Der Spiegel, was denied accreditation by Turkish authorities and forced to leave the country.