The United Nations has come under fire from Turkish officials and media outlets this week after signing a deal stop the use of child soldiers with the Syrian Democratic Forces (SDF), a group dominated by Kurdish militants from the Peoples' Protection Units (YPG).

Virginia Gamba, the UN Secretary General's special representative for children and armed conflict, met with SDF general commander Mazloum Abdi in Geneva over the weekend to sign an action plan agreeing to stop recruiting child soldiers and remove any currently fighting in its ranks.

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Turkish officials, however, zeroed in on the decision to sign an agreement with Abdi, who is on Turkey's most wanted list and has professed to serving in the outlawed Kurdistan Workers' Party (PKK). Abdi is also known as Ferhat Abdi Şahin, Şahin Cilo and Mazlum Kobane.

Turkish officials condemned the decision to sign an agreement with the SDF, which Ankara views as an extension of the YPG and thus the PKK.

The Syrian Kurdish fighters are known to have links to the PKK, which has carried out an armed struggle for Kurdish self-rule in Turkey since the 1980s.

Gamba called the new agreement with the SDF an "important day" that "demonstrates a significant commitment by the SDF to ensure that no child is recruited and used by any entity operating under its umbrella".

The use of child soldiers by various sides in the Syrian conflict has been singled out as a serious cause for concern by the UN and human rights agencies.

A Turkish Foreign Ministry statement called Gamba's meeting with Abdi "at the UN Office in Geneva without the knowledge of the members ... a grave incident which we strongly condemn".

Turkey's state-run Anadolu Agency called the agreement "a sinister subterfuge meant to legitimize a bloody terrorist organization that has killed tens of thousands of people."

The PKK is classified as a terrorist organisation by Turkey, the United States and other countries, as well as the European Union.

However, only Turkey defines the YPG and SDF as terrorist groups.

The Syrian Kurdish militias have been at the heart of one of Turkey's ongoing disputes with the United States, which joined forces with the groups in an international coalition to defeat the Islamic State.

The aftereffects of that conflict continue to sour Washington's relations with Ankara, which has demanded that U.S. forces withdraw from the northern Syrian territories controlled by the YPG and SDF and create an elusive "safe zone" on the Turkish border that is free of the Kurdish