“An agreement was signed between our units and Russian forces operating in Syria that will train us in modern military tactics," YPG spokesman Redur Xelil said on Monday.
“This is the first agreement of its kind, although we have had previous cooperation [with the Russians] in Aleppo city," he added.
He said the agreement was part "of the framework of the fight against terrorism," adding that it was signed on Sunday and came into effect on Monday.
Xelil noted that Russian troops were already present at the training camp in the Afrin region, one of the three "autonomous" cantons which is under the control of the Kurdish authorities.
It is likely that the Russian agreement with the YPG, who are currently in control of nearly all of Syria’s entire northern border with Turkey, would anger Ankara.
Turkey considers the Kurdish forces to be a "terrorist" group and an extension of the outlawed Kurdistan Workers' Party (PKK).
The YPG make up the bulk of the so-called Syrian Democratic Forces (SDF), a US-backed coalition of fighters who have seized swathes of territory from Daesh terrorist group in northern Syria.
Founded in October 2015, the SDF is comprised mostly of Syrian Kurds, numbering at least 25,000. It receives equipment, weapons and air support from the US.
Washington has been sponsoring anti-Damascus groups operating in Syria by labeling them as moderate militants.