Turkish officers on the Syrian border have communicated with Islamic State militants in Iraq and Syria, Turkey's Cumhuriyet daily reported, citing an investigation by the Ankara Chief Prosecutor's office which allegedly eavesdropped on their phone calls.

The wiretapping reportedly took place last year as part of an investigation into six missing Turkish citizens, the Cumhuriyet reported. The relatives of those missing believed they might have joined the ranks of Islamic State (IS, formerly ISIS/ISIL) militants.

An investigation was launched into as many as 27 suspects, some of them in Syria, the report revealed.

The Chief Prosecutor's office reportedly received permission to wiretap the phones of 19 people who were thought to have put the six missing persons in touch with Islamic State. The investigation reportedly revealed that those who wanted to join IS ranks received some form of “ideological training.”

The file on the investigation is said to have been handed over to the Military Prosecutor's office in March, after the Ankara Prosecutor's office deemed the issue outside of its jurisdiction, according to the Turkish newspaper.

“Those [who joined ISIS] from Ankara often used [the] Elbeyli district [of Kilis] as a throughway by traveling via Gaziantep and Kilis to the village of Able, which is subordinated to Syria's Al-Bab district,” the report said, as cited by newspaper Today’s Zaman.

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A note written in one of the transcripts for the wiretappings allegedly states that the person designated in the transcript as “X2” is considered to be a member of the military, the Cumhuriyet reported.

One of the conversations is said to be as follows:

--Yes, brother.

X2: We are on the mined land where I delivered the vehicle. We have put our lights on. [We have the] material on us; come here with your men from that side…

Ankara has recently faced a number of accusations alleging it has bought oil from IS and let terrorists freely pass through Turkey's border with Syria. A newly-leaked report on illegal oil sales by Islamic State, compiled at the request of Norway, revealed that most of the IS-smuggled oil has been destined for Turkey, where it is sold off at bargain low prices.

In early December, the Russian Defense Ministry also released evidence which it said shows most of the illegal oil trade by IS goes to Turkey. Ankara has denied the allegations.

READ MORE: Ankara must come clean & address mounting evidence of links with ISIS – Iraqi MP to RT

Iraqi MP and former national security adviser, Mowaffak al Rubaie, told RT on Tuesday there is “mounting evidence” from all over the world, including Iraq, that “Turkey is playing not a very clean game,” when it comes to Islamic State.

“Turkish authorities need to do a lot more than what they are doing now to come clean from the accusations that they are siding [with], or at least that they are turning a blind eye to, the movement of these terrorists from Turkey to Syria and Iraq and vice versa,” the MP said.