Turkey is planning strict security measures for the summit. Among other things, authorities announced on Monday that all demonstrations will be banned from June 28 until the summit, which will be held on July 7-8.
Of those arrested, 185 are suspected of membership in various left-wing organizations, including the left-wing extremist DHKP-C, which has previously claimed responsibility for attacks in Turkey. Others are suspected of links to IS.
On Tuesday, Turkish prosecutors ordered the arrest of 241 suspects. 209 of them were subsequently taken into custody in raids at several locations in Ankara, according to a statement from the Chief Public Prosecutor's Office.
