Assyrian Christian priest Sefer Bileçen, the sole caretaker of Mor Yakup Monastery, a 1,500-year-old church in Turkey's southeastern city of Mardin, was arrested on Friday after detained in Turkish army's operation in the region.

"Assyrian priest Bileçen, who was detained yesterday, was arrested," journalist Sedat Sur said on Twitter. But, he did not mention the reason behind the priest's arrest.

Bileçen, alongside with two other Assyrians Joseph Yar and Musa Taştekin, were detained on Thursday during a raid by Turkish soldiers in and around the Assyrian settlement Üçköy, Gazete Duvar said.

"We still do not know why Father Sefer, Joseph, the village headman, and others were detained. The lawyers are involved but no information was given, saying there was a secrecy decision on the file," the news site quoted Yuhanna Aktaş, the president of Mardin Assyrians Union, as saying.

"We do not understand why a priest is detained," Aktaş said.

During World War One, Assyrians alongside Armenians were subjected to massacres and forced displacement, recognised by many -- though not by Turkey -- as genocide. This, and ongoing discrimination decades later drove many thousands to seek safety abroad.

As a result, although there are only around 25,000 Assyrians left in Turkey. And, the conflict between Turkish armed forces and the Kurdistan Workers' Party (PKK), which has been fighting since 1984 for self-rule in Turkey's mainly Kurdish southeast, where the Assyrian population is mostly found. Many Assyrians have found themselves caught between the two sides.

Besides the issues of security, Turkey's Assyrians face issues related to their identity in a country that stridently promotes its official language, Turkish, at the expense of other native languages, including the Assyrian mother tongue, Aramaic.