A 20-year-old British man is reported to have been killed in Syria while fighting for the PKK-affiliated Democratic Union Party's (PYD) armed wing, the People's Protection Units (YPG).

According to an article published on British daily The Guardian, 20-year-old Ryan Lock was reportedly killed in Syria during the terrorist group's Raqqa operation. The article states that the YPG had informed Lock's family "he died along with four other fighters on December 21."

Lock is believed to have joined YPG ranks on Sept. 4, though his motives to fight with the group remain unknown.

The YPG is considered to be a terrorist group by Ankara as the Syrian offshoot of the outlawed PKK, which is recognized as a terrorist group by the U.S., EU and other international organizations.

Despite Ankara's warnings and concerns, Washington has been working closely with the YPG and supplying arms, according to the Turkish government. Months ago, the YPG launched a ground operation in Syria to capture Daesh's so-called capital Raqqa.

Back in September 2016, three American citizens were also killed fighting for the YPG. According to an Associated Press (AP) report, the caskets of the three men, Levi Shirley, 24, Jordan McTaggart, 22, and William Savage, 27, arrived in Chicago from Syria in September while the bodies of Shirley and MacTaggart were afterwards transported to Denver by train.

The YPG has repeatedly targeted NATO member Turkey's tanks in Syria. A Turkish soldier was killed and three others were injured in a rocket attack by the U.S.-sponsored YPG terror group in late August 2016. While the U.S., considered a significant ally to Turkey, refers to the YPG as "a strong partner," the PKK-affiliated group released a video in late January 2016 in which Westerners were called on to join the group and attack Turkey. The footage shows a man, who had his face covered with a scarf and carrying a rifle, making a statement to a group gathered around him, urging Kurds and Westerners to take up arms against the Turkish state. Even though the YPG is supported by the Obama administration, Ankara has already hinted at the possibility of launching an operation on the YPG-held town of Manbij.