Turkish Presidential Spokesman Ibrahim Kalin and US National Security Advisor John Bolton held a phone conversation Wednesday over the safe zone plan in Syria, the presidential office said in a statement.

The Turkish presidential aide told Bolton that Turkey has completed its preparation for the implementation of the joint Turkey-US operations in Syria without delay, according to the statement.

The two officials also discussed bilateral trade, fight against terrorist and the last situation in Syria, it added.

On Aug. 7, Turkey and the United States agreed to set up an operation center to coordinate and manage the planned safe zone, which is expected to serve as a "peace corridor" to facilitate the return of displaced Syrians.

However, Turkey has constantly voiced concerns over the US delay in implementing the plan.

Turkey and the United States have been at odds over the northeastern Syria and the YPG, the Syrian offshoot of the Kurdistan Workers' Party, which is listed as a terrorist organization by Turkey, the United States and the EU.

However, the United States has allied itself with the YPG in the fight against the Islamic State in Syria.