Turkey's Security General Directorate sent related provincial police departments a message warning that the PKK had sent three people who would probably conduct suicide attacks from the Southeast to major cities, CNNTurk said.

In the message, the general directorate wanted the police departments to increase efforts to capture the suspects.

The message also urged citizens to inform authorities of suspicious situations.

The report came just hours after two percussion bombs exploded in central Istanbul on Tuesday, causing little damage.

Percussion bombs typically make a loud noise but rarely cause serious damage. No claim of responsibility was reported for the bombings.

The attacks came one day after police raided the hideout of a left-wing militant organization, killing a senior member. One police officer and a civilian died in that raid.

Photo is an archive image.