The operation was based in Istanbul but also saw detentions in other provinces.

During a search of premises at Istanbul University and suspects’ houses, police found 10 one-U.S.-dollar bills believed to have been sent by Pennsylvania-based Fetullah Gulen to help members recognize each other.

Many detained FETO suspects' dollar bills have been added to evidence by Turkish police who believe the serial-number letters on the banknotes are used as code within the organization.

Other provinces covered by the operation include Tekirdag, Kocaeli, Denizli and Kirklareli.

The deadly coup attempt began late July 15 when rogue elements of the Turkish military tried to overthrow the country's democratically-elected government, killing at least 246 people and injuring more than 2,100 others.

The government said the attempted coup was organized by followers of Gulen.

Gulen is accused of a long-running campaign to overthrow the state through infiltrating Turkish institutions, particularly the military, police and judiciary, forming a ‘parallel state’.