Prime Minister Ahmet Davutoğlu on Wednesday said that secret actors are behind the deadly suicide attack carried out by a Daesh terrorist in Istanbul, which left 10 people dead. Davutoğlu held a press conference at Istanbul Governorate and underscored Turkey's determination to fight terrorism and find the perpetrators."Secret actors are behind Istanbul attack" Davutoğlu said and added that Turkish security forces are trying to reveal who used Daesh as a 'subcontractor.'He accused the Assad regime of openly cooperating with the terrorist organization and said that Daesh militants were transferred to Northern Syria to fight moderate opposition with the help of Assad regime. He said that nobody should think about punishing the civilian population in Syria and the moderate opposition forces for the sake of assisting Daesh."Certain foreign powers have an obstructing stance against Turkey's airstrikes on Daesh targets" Davutoğlu said, implying that Russian air force appears to be protecting Daesh within Syrian air space.Davutoğlu also said that Turkish security forces have detained four suspects in connection with the deadly Istanbul blast. A total of five suspects have been detained in connection with the blast, as Interior Minister Efkan Ala said that a suspect with a link to the attack had been detained in Istanbul late Tuesday.Speaking about his visit to the hospital to see victims who were injured in the attack, Davutoğlu said that Turkey is ready to give citizenship to those who were injured in Istanbul blast.Davutoğlu said that the suicide bomber entered Turkey as a refugee, and his movements were not monitored as he was not on watch list.He underscored that Turkey will take more visible security measures in densely populated areas after Istanbul blast.An explosion occurred in Istanbul's Sultanahmet Square early Tuesday killing 10 and injuring 15. Officials have announced that the attack was carried out by a Syrian suicide bomber and that he was not on the police watch list.