A cutting tool comprising a cutting tool holder and a cutting insert adapted to be mounted thereon. The tool holder comprises an insert seat defined by a base and at least one side wall extending from the base to define an insert seat space adapted to receive therein the insert. The seat comprises a support element extending into the insert seat from the base, and a fastening member engageable with the seat. The fastening member is displaceable with respect thereto between a mounting position adapted to allow the insert to be mounted onto the seat and a securing position adapted for securing the insert within the seat. The insert is formed with a securing cavity and when the insert is mounted onto the tool holder and is in the securing position, a portion of the support element and the fastening member is received within the cavity of the insert.