The United States have secretly armed its main proxy group in northern and eastern Syria, the Syrian Democratic Forces (SDF), with anti-tank and anti-aircraft missile systems, Sputnik reported on January 5.

The Russian news agency said that the U.S.-led coalition delivered BGM-71 TOW anti-tank guided missiles (ATGMs) and unidentified man-portable air-defense systems (MANPADs), possibly FIM-92 Stingers, to the Kurdish-led group in mid-December.

Prior to the deliveries, the coalition trained some 80 fighters of the SDF on the systems at a base near the city of al-Qamishli in the northern al-Hasakah countryside.

Sources in the SDF told Sputnik that most of these ATGMs and MANPADs were deployed at Rifaat, Manbij and Kobane in the northern and northeastern countryside of Aleppo. Turkey threatened to attack the three key towns on multiple occasions in the past, most recently in November after a deadly bombing in Istanbul that was blamed on the core faction of the SDF, the People’s Protection Units.

“This is the first time that the U.S. Army has delivered these types of missiles to its allies in the SDF since its entry into the east of the Euphrates [River],” the news agency quoted its sources as saying.

If confirmed, the U.S. move would significantly boost the military capabilities of the SDF, which is currently facing threats from both Turkey and the Syrian government of President Bashar al-Assad.

The U.S. may have decided to supply these advanced missile systems to the SDF in response to Russia’s ongoing efforts to restore ties between Turkey and Syria.

In December, the defense ministers and intelligence chiefs of Ankara and Damascus met in Moscow. A more important meeting between the foreign ministers of the two countries will be held in mid-January. In addition, Turkish President Recep Tayyip Erdogan have already voiced his readiness to meet with Assad later this year.

Any military coordination between Ankara and Damascus will pose an existential threat to the SDF. The group could quickly lose its remaining areas in Aleppo and Raqqa because the U.S.-led coalition no longer has bases there. Washington’s indirect military support will not likely be enough to allow the group to survive for too long.