BERLIN (Reuters) - Germany has granted asylum to four Turkish soldiers, including one Ankara accuses of playing a leading role in the failed military coup of July 2016, in a new setback for relations between the two countries, weekly magazine Der Spiegel reported.

By granting them asylum, German authorities make it impossible for them to be extradited to face charges, a refusal likely to dismay Turkish authorities, who accuse them of treachery and membership in a terrorist organization.

Turkey accuses Ilham P., a former Turkish colonel whose surname cannot be published in full because of German privacy practices, then head of the Ankara military academy, of being ring-leader of the group.

Germany’s Interior Ministry said it could not comment on individual cases for data and personal protection reasons.

Relations between European countries and Turkey have become increasingly strained following President Tayyip Erdogan’s large-scale crackdown on suspected supporters of the coup. Some European politicians and human rights groups say the crackdown shows Turkey is sliding into authoritarian rule.

Turkish authorities have jailed more than 50,000 people and sacked or suspended more than 150,000 since the coup, which Ankara blames on supporters of a Muslim cleric living in self-imposed exile in the United States.

The government says such measures are necessary given the multiple security threats it faces. The cleric, Fethullah Gulen, denies involvement in the coup, in which 250 people were killed.

Dozens of German nationals have been detained in Turkey over the past two years, some of them for alleged links to the coup plotters.

Earlier on Friday, a Greek court ruled that a man accused of being behind a series of suicide bombings in Turkey could not be extradited because his life would be in danger back at home.