Turkey on Tuesday strongly condemned an agreement signed between the United Nations and the Syrian Democratic Forces (SDF), which is controlled by the People's Protection Units (YPG) terror group in Syria, to end the recruitment of child soldiers.

Virginia Gamba, the U.N. secretary-general's special representative on children in armed conflicts, met with YPG commander Mazloum Abdi — also known as Ferhat Abdi Şahin or Şahin Cilo, who is on Turkey's most-wanted list — and signed an agreement over the weekend in Geneva.

The so-called agreement aims to end SDF's use and recruitment of individuals under the age of 18. The group has been long known to recruit and use children between the ages of 11 and 18 in its ranks.

The YPG, which works under the label of the SDF, is the Syrian branch of the PKK that is a designated terrorist organization in Turkey, the EU and the U.S.

The high-level U.N. officials told Anadolu Agency (AA) that they were not informed about the controversial deal with the terrorist group. Also, the agreement was signed on Saturday with the participation of a few attendants when the U.N.'s Geneva office was on a break over the weekend.

Gamba said the agreement was being made to ensure "no child is recruited and used by any entity operating under its umbrella."

The Turkish Foreign Ministry responded with a statement strongly condemning the U.N.'s meeting with Ferhat Abdi Şahin and the agreement, calling it a "grave development."

"The signing of an agreement by the U.N., which should be at the forefront in the fight against terror, with a terrorist organization cannot be explained in any way. This is also a clear violation of the UN's own decisions on terrorism," the Foreign Ministry said.

The ministry said the nature of the agreement once again attests to the severe violations of human rights and international law committed by the SDF.

"However, it is absolutely unacceptable for the U.N. to negotiate with the bloody terrorist organization to solve this problem," the ministry underscored.

U.N. spokesman for the Secretary-General Stephane Dujarric said in a press conference Monday that Gamba's plan with the YPG-led group "does not imply any legitimacy, political legitimacy, for any armed group that she engages in."

A high-level official in the U.N. Geneva office told AA that it has not been informed about the meeting with the YPG representative. Also, Alessandra Vellucci, U.N. spokeswoman in Geneva, said the deal was not publicized due to security reasons. After she was reminded that Syrian meeting in Geneva office, in which hostile parties came together, had been announced, Vellucci stressed that each meeting has its own specifications.

The PKK has waged a terror campaign against Turkey for more than 30 years and been responsible for the deaths of nearly 40,000 people, including women and children.

The activities of the YPG terrorist group have been a major security concern for Ankara, while the U.S. viewed the group as a "reliable partner" in the fight against Daesh. Şahin, a PKK terrorist on Turkey's most wanted list, has been an integral part of this partnership, leading initial negotiations with the U.S. beginning in August 2014.

Şahin was the leader of the YPG before assuming the role as commander-in-chief of the U.S.-backed SDF last year. He has been a member of the PKK for decades, working in Syria, Iraq and Europe. Şahin is strongly supported by Abdullah Öcalan, the jailed leader of the PKK terrorist group.

The YPG's use of child soldiers in its ranks has repeatedly been documented and criticized by international human rights organizations, including Amnesty International and Human Rights Watch. The group reportedly tricks families into giving up their children or kidnaps the children, taking them to training camps, where they are denied contact with their families.

According to a report published by Anadolu Agency in April, to ensure the commitment of the children, the YPG makes children and youngsters addicted to drugs, so they can later be used as suicide bombers and fight on the front lines.

In 2018, a U.N. annual report on children in armed conflict revealed 224 cases of child recruitment by the YPG between January and December in 2017, a fivefold increase compared to previous years.

Human Rights Watch also documented that the terrorist organization continues to recruit children despite objections from families and children while preventing families from getting in touch with their children.

The organization documented 59 children soldiers between the ages of 10 and 15, adding that the YPG confirmed integrating children into the organization.

Human rights organizations have also documented the YPG's violations of human rights, including torture and deliberate disruption of education and health services.

In March 2018, a YPG training camp in Afrin that was destroyed by Turkish forces in Operation Olive Branch was screened by Anadolu Agency. Investigations revealed that the camp was a center for training 13-to-17-year-old recruits to the terror group.

On March 22, 2018, a 17-year-old YPG fighter named Yasemin Arif, who was forced into the group at age 14, died in clashes in Deir el-Zour.

The 1949 Geneva Convention on the Protection of Civilian Persons in Time of War prohibits the use of children under age 15 as soldiers.