Story highlights The deal could be viewed as a sign of eroding US influence in Syria

The new agreement is likely to further complicate the picture in Northern Syria

Washington (CNN) Some of America's most critical allies in the fight against ISIS have made a deal to cede territory to Russian and Syrian government troops in northern Syria, the Pentagon confirmed Friday.

The Manbij Military Council, a key US ally in Syria, has permitted Russian and Syrian regime forces to take over villages near the town of Manbij, according to a defense official.

US military officials said the purpose of the deal was not immediately clear. But as a result, US military advisers could soon find themselves in close proximity to Syrian and Russian troops. The advisers are currently training local forces in Manbij to combat ISIS in the vicinity, part of the approximate 500-strong contingent of American Special Operations Forces in Syria.

A spokesman for the US-led military coalition confirmed Saturday that additional international troops had been deployed in and around Manbij after images of coalition armored vehicles appeared online.

Col. John Dorrian wrote on Twitter that the coalition "has taken this deliberate action to reassure coalition members and partner forces, deter aggression and keep focus on defeating ISIS."

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