Turkish police arrested nine alleged members of the Islamic State extremist group on Wednesday, less than one day after a suicide bombing killed 10 foreigners, including eight Germans, in the touristic heart of Istanbul.
Three Russian citizens were among those arrested in the raids, which took place in the coastal Izmir province and Antalya province in the south, the Dogan news agency reported.
Turkish officials, who have pinned responsibility for the attack on Islamic State, had said a man who crossed into the country from Syria carried out the bombing Tuesday morning in the Sultanahmet area, an historic part of the city home to the famed Blue Mosque and Hagia Sophia museum.
On Wednesday, the Saudi-owned al-Hayat newspaper reported that the alleged suicide bomber, 27-year-old Nabil Fadli, was born in Saudi Arabia but left with his family when he was eight-years-old. He held Syrian citizenship, the report added.
No group has yet claimed responsibility for the attack.
Turkish authorities blamed two major suicide bomb attacks last year on Islamic State militants. Though the Sunni extremist group has claimed recent bombings and killings in Egypt, Iraq, Syria, Libya, Tunisia, Saudi Arabia and Kuwait, it has never taken responsibility for any inside Turkey.
Turkey last year stepped up efforts to tackle Islamic State, which holds territory in neighbouring Iraq and Syria, after a period in which the government was criticized for being slow to counter the militia and close its porous border.
Hurriyet newspaper in Turkey said the country's intelligence services had warned the security forces twice in the weeks before the attack about the possibility of a suicide attacks targeting foreigners in the weeks before the blast hitting the tourists.
German's Interior Minister Thomas de Maiziere is expected in Turkey on Wednesday. Chancellor Angela Merkel, who condemned the "murderous act" in Istanbul, has already spoken with Turkish President Recep Tayyip Erdogan by telephone.