Turkey has arrested two more people in connection with the suicide bombing this week which killed 10 German tourists in Istanbul, Interior Minister Efkan Ala said Thursday.
This raises the total number of arrested in connection with the investigation to seven.
Police have also carried out numerous raids against Islamic State cells in various parts of the country.
Authorities are holding the extremist group responsible for the bombing which took place near the iconic Blue Mosque and Hagia Sophia in the Sultanahmet district.
Islamic State, which normally claims its international terrorist attacks, has never taken responsibility for attacks in Turkey.
There is increased security in tourist areas of Istanbul, with the government deciding to boost police presence after the attack.