ALEPPO — The Syrian regime and the armed opposition recently conducted their third prisoner exchange in six months, swapping nine detainees from each side, as hundreds of thousands are thought to remain imprisoned.

The exchange took place April 22 at Abu al-Zandeen crossing, near al-Bab in northern Aleppo province. The crossing separates the opposition areas from the government-held ones.

Turkey's state-run media, Anadolu Agency, cited an April 22 statement by the Turkish Foreign Ministry confirming the swap was the third to be carried out under the auspices of a working group formed as part of the Syrian peace talks led by Turkey, Russia and Iran, and with the participation of the United Nations. The group addresses releasing detainees and abductees, recovering bodies and identifying missing persons.

On Feb. 12, the Free Syrian Army (FSA) and the Damascus government exchanged 20 prisoners from each side. The first exchange took place in November, when Anadolu Agency reported, “The regime forces released 10 prisoners in exchange for the FSA releasing 10 detainees as well.”