BERLIN (Reuters) - Turkey has arrested a Turkish lawyer hired by the German Embassy in Ankara, a diplomat at the Foreign Ministry said on Wednesday, a measure that could further raise tensions between the NATO partners.

Relations between the two countries have been strained over German criticism of President Tayyip Erdogan’s crackdown on suspected opponents after a failed coup in 2016 and Turkey’s military offensive last month against Kurdish militia in Syria.

“We are intensively trying to find out what the accusations are and to lift the remand,” said the German official, declining to be named. “The detention is incomprehensible.”

The lawyer was arrested in mid-September, the official said.

The lawyer had been hired by the German Embassy to provide documents related to Turkish citizens who had applied for asylum in Germany, German media reported.

The number of Turks seeking asylum in Germany has risen since the 2016 failed coup that Erdogan says was planned by supporters of U.S.-based cleric Fethullah Gulen who were deeply embedded in Turkey’s institutions.

Between January and October this year some 9,500 Turks applied for asylum in Germany, up 8% from the same period last year, official figures show, making Turks the third-largest group of asylum seekers after Syrians and Iraqis.