The move by Damascus ally Moscow comes after Ankara launched air strikes on Kurdish targets in Syria and Iraq on November 20, a week after a deadly Istanbul bombing that it blamed on Kurdish militants, who have denied responsibility.
Residents of Tal Rifaat, a Kurdish-held pocket north of Aleppo, told AFP that Russian troop reinforcements had reached the city.
Tal Rifaat lies 15 kilometers (nine miles) south of the border with Turkiye. Kurdish forces control the city and surrounding villages, and Russian troops were already present in the area.
Residents said Russian forces had set up roadblocks at a nearby village separating it from positions under the control of Turkish forces and their Syrian rebel proxies.
Turkish proxies control areas surrounding Tal Rifaat from the north, while Russian-backed Syrian troops control zones mostly to the south.
After carrying out a series of air strikes, Turkiye has threatened to launch a ground incursion into northern Syria, including the Tal Rifaat pocket as well as Kobani and Manbij further east.
Kobani and Manbij are under the control of the US-backed Syrian Democratic Forces (SDF), which include the Kurdish People’s Protection Units (YPG), one of the groups Turkiye accuses of being behind the Istanbul bombing.
The Syrian Observatory for Human Rights, a Britain-based war monitor, said Russia was also reinforcing its troops at a government-controlled air base near Tal Rifaat.
The reinforcements could be an attempt “to stop or put off the Turkish operation,” Observatory chief Rami Abdel Rahman told AFP.
Kurdish-led forces in northern Syria have called on Russia to dissuade Turkiye from launching a ground offensive against them, their commander said on Tuesday.
The Observatory said Russian reinforcements had also reached the outskirts of the border city of Kobani.
Russian troops deployed in some Kurdish-controlled border areas of northern Syria following a 2019 agreement that sought to avert a previous Turkish incursion threat.
President Recep Tayyip Erdogan said last week that Turkiye was more determined than ever to secure its border with Syria from attacks by Kurdish fighters, threatening a ground operation “at the most convenient time.”
Since 2016, Turkiye has carried out successive operations against Kurdish forces in northern Syria that have installed its proxies in several areas along the border.