The Russian Defense Ministry's Syria reconciliation center said on Thursday that six American MRAP-type armored vehicles had taken an "uncoordinated route and without prior notice" in the Kurdish-held Syrian province of Hasaka.

Rear admiral Alexander Karpov, the reconciliation center's deputy head, said in the statement that Russia's military police patrol had stopped the U.S. convoy as it traveled west along the M-4 highway and told it to head back in the opposite direction.

Karpov described the incident, also reported by news agencies, as "another case of violation of the de-confliction protocols by the units of the U.S. armed forces illegally located in Syria."

Moscow has long insisted that the U.S. military presence in Syria is illegal and has been firm in its backing of Syrian President Bashar al-Assad, helping him gain the advantage in a protracted civil war.

State-run news agency Tass reported that the Pentagon had declined to comment on the latest incident which comes as relations continue to deteriorate between Russia and the U.S. Newsweek has contacted the Pentagon for comment.

Tass had earlier reported that a joint statement by the coordination headquarters of Russia and Syria said the actions of the United States in the territories under its control could "lead to further radicalization of the people living there." It referred in particular to the Syrian refugee camp of Al-Hol in northern Syria.

Adding to the mix of tensions between Moscow and Washington amid diplomatic expulsions, claims of election interference and sanctions, is a dispute over the conduct of Russian and American forces in Syria.

The U.S. military is working with coalition troops inside Syria to help Kurdish and Arab forces fighting the Islamic State militant group (ISIS) in the north and the east of the country.

But in an assessment presented to U.S. Congress this month about Operation Inherent Resolve, the international campaign to tackle ISIS, the Pentagon accused Russia of violating "de-confliction processes" in Syria's northeast.

Although it concluded that Russia "did not pose a threat to coalition forces," the report said that Russia "seeks to harass and constrain U.S. forces with the ultimate goal of compelling U.S. forces to withdraw from northeastern Syria."

However, Russia immediately hit back at the report, with its embassy in Washington, D.C. tweeting that the U.S. presence in Syria "is illegal in the first place," and as such, "does not have any right to criticize legitimate actions of the Russian Armed Forces"

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