Two of the persons who participated in the attack on the Crocus City Hall concert hall in the Moscow region had visited Turkey, but there was no warning from Moscow about them, Hurriyet daily reports, referring to its sources.

Two of the four arrested terrorists had traveled the Russia-Turkey-Russia route before; they had arrived in Turkey from Moscow. At the same time, they have no registration—residence permit, or any other documentary proof of legalization—in Turkey.

The sources added that there were no warnings from Moscow regarding these persons. The facts of their presence in Turkey are being "studied very carefully" and will continue to be communicated to the Russian side.

"Ankara carefully studied all the matters related to these two persons and reported everything to Moscow," Hurriyet notes.

It adds that the Turkish side expects that Russia will strengthen the exchange of information about the activities of the Islamic State (IS) terrorist group and its offshoot IS-Khorasan, as they are equally a threat to Turkey.