The two suspects who have not been identified were killed in a police operation in the capital Ankara yesterday, hours before the Justice and Development Party's congress was due to begin.
Ankara governor Ercan Topaca said today that police seized sketches and diagrams indicating they aimed to target the congress as well as events organised by civil society groups.
Turkey has been hit by a string of attacks blamed on IS and Kurdish militants since 2015. On New Year's Eve, a gunman killed 39 people in an Istanbul nightclub. IS claimed the attack.