Moscow has agreed to train Kurdish militias at a camp in Afrin, YPG spokesman Redur Xalil said in a statement, and opens up the possibility of Russian expanding its influence into Syria's most prominant anti-Islamic State group, which has been heavily backed by the US.
"An agreement was signed between our units and Russian forces operating in Syria that will train us in modern military tactics," Xalil told AFP.
Moscow will set up a military base in the Kurdish-controlled town, he said, as Russian military police entered Afrin on Monday.
Masked Russian troops and armoured vehicles were spotted patrolling the city alongside Kurdish forces.
It comes as rumours emerge that Moscow is looking to extend its influence into the US-backed anti-IS coalition known as the Syrian Democratic Forces.
The group is dominated by Kurdish fighters and has led the most successful campaigns against IS in Raqqa and Aleppo provinces
Despite Moscow's massive military involvement in Syria - supporting the regime - it has been sidelined in areas of northern Syria outside Damascus' control by the US.
US President Donald Trump has said he will ramp up support for the anti-IS force and more American troops are set to head for Syria to support the Syrian Democratic Forces.
These fighters are ready to launch a massive offensive on Raqqa - IS' self-declared "capital" - and Moscow is believed to be concerned about being excluded from the campaign.
Moscow is expected to deny the move, but experts told The New Arab that the Afrin base could be a way of Russia extending its influence into Kurdish areas.
It will also likely anger Russia's ally Turkey. Ankara is supporting Syrian rebels fighting IS in northern Syria but whose forces are surrounded by two Kurdish cantons.