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"Certain individuals" were exchanged simultaneously in northwest of Syria, near the town of Al-Bab close to Aleppo, the ministry said, calling it a "pilot project".

While it did not give a precise figure of detainees involved, the British-based Syrian Observatory for Human Rights, which relies on sources in Syria, said 10 prisoners from each side were exchanged.

Russia, Iran and Turkey are working to implement the Russia-sponsored Astana process. 

Each country plays a key role in the conflict that started in March 2011. Russia and Iran have intervened on the side of Syria's regime, ensuring its survival, while Turkey supports rebel groups in northern Syria to prevent Syrian Kurds establishing and expanding territory along its border.  

All of them say they are fighting Islamic State fighters and other jihadists in the northern regions. 

In September, Turkey and Russia agreed to set up the Idlib buffer zone to avert a Syrian regime offensive, but jihadists who hold around 70 percent of the area have refused to withdraw.

The Astana process was launched after Russia's military intervention in Syria tipped the balance in the regime's favour. It has gradually eclipsed an earlier UN-sponsored negotiations framework known as the Geneva process.  

The US and EU are opposed to Assad staying on as well as the presence of Iranian and Iranian-commanded fighters in Syria.  

The Syrian conflict began when Assad's regime responded with military force to peaceful protests demanding democratic reforms during the Arab Spring wave of uprisings, triggering an armed rebellion fuelled by mass defections from the Syrian army.

Hundreds of thousands of civilians have been killed in the war, mostly by the regime and its powerful allies, and millions have been displaced both inside and outside of Syria.

Turkey of late has become quieter about its initial stated aim of seeing Assad leave power as it has stepped up cooperation with Russia over Syria.