ANKARA (Reuters) - Turkish authorities on Tuesday detained an adviser to the head of the main opposition party over suspected links to the July coup, the Hurriyet newspaper said, the first time someone close to the senior ranks of the secular opposition has been targeted.

Fatih Gursul was detained on suspicion of having used the ByLock smartphone messaging app, Hurriyet said. The government says ByLock was used as a communication tool by supporters of the Muslim cleric whom it blames for the failed putsch.

At a news conference in the parliament building, the opposition Republican People’s Party (CHP) Deputy Chairman Ozgur Ozel said that Gursul was an unpaid senior adviser to the head of the party, Kemal Kilicdaroglu.

Ozel did not say whether Gursul had been detained, but accused the government of failing to share information.

“What we have been saying for months is that the state should share any information or documents on Gursul with the CHP if they have it, but there has been no contact or sharing with the CHP despite our calls,” Ozel said.

The detention raises concerns that the secular opposition may be targeted in the government’s widening crackdown that has followed the abortive coup.

The Istanbul prosecutor’s office, which Hurriyet said had issued the detention order, declined to comment.

Turkey’s state intelligence agency has cracked ByLock’s security features and say it has traced thousands of people it alleges are linked to the coup.

Some 36,000 people have been jailed following the coup, and 125,000 military officers, police, teachers, judges, prosecutors and others have been sacked. Rights groups and some of Turkey’s European allies fear President Tayyip Erdogan is using the coup as a pretext to crush dissent.

The government says such measures are necessary to root out supporters of the cleric, Fethullah Gulen. Gulen, who has lived in self-imposed exile in the United States since 1999, has denied orchestrating the coup, and condemned it.

Separately, arrest warrants were issued for another 36 judges, prosecutors and judiciary personnel on Tuesday in the southeastern province of Diyarbakir over suspected links to Gulen’s network, the provincial prosecutor’s office said.

Authorities also detained two mayors from the sister party of the pro-Kurdish Peoples’ Democratic Party (HDP) in Diyarbakir over alleged links to the outlawed Kurdistan Workers’ Party (PKK), according to a statement from the local prosecutor’s office.