The government has blamed a Syrian Kurdish group classified as a terror organisation by Ankara as well as homegrown Kurdish militants for the car bombing on Wednesday in the heart of the Turkish capital.
Twin bombs kill 86 at pro-Kurdish rally in Turkish capital
A total of 17 suspects have now been detained after nationwide raids in the wake of the attack, with one more still on the run, the official Anatolia news agency said, quoting Ankara prosecutors.
President Recep Tayyip Erdogan had said on Wednesday that 14 suspects had been detained.
"The case has almost been solved. State officials will soon make the necessary announcements," Ankara chief prosecutor Harun Kodalak was quoted as saying.
Prime Minister Ahmet Davutoglu laid carnations on Friday in memory of the victims at the site of the blast in an area housing a string of public institutions including parliament and the army headquarters.
Davutoglu and Erdogan both said the attack was a joint operation of the outlawed Kurdistan Workers' Party (PKK) in cooperation with the Syrian Kurdish People's Protection Units (YPG).
18 killed in Ankara car bomb attack on military
The focus on the Syrian Kurdish fighters is threatening an open dispute with Turkey's NATO ally the United States, which classifies the PKK as a terror group but works with the YPG as an effective force in the fight against militants in Syria.
The Anatolia report said investigators were focusing on the links of those detained to the PKK. It said the raids took place in cities from Izmir on the Aegean to Diyarbakir in the mainly Kurdish southeast.
Davutoglu said the bomber was a Syrian national who according to press reports slipped into Turkey along with refugees from Syria's civil war.
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