Russia is aiming to prevent the U.S. from undercutting Syrian President Bashar Assad through the new policies for the country outlined by Secretary of State Rex Tillerson.

“Rex Tillerson has said many times that the only goal, the only reason is to defeat [the Islamic State in Syria],” Russian Foreign Minister Sergey Lavrov told reporters Friday. “Now, they have even more far-reaching plans, and we'll have to keep that in mind and try to find ways that would prevent [them] from undercutting the sovereignty of the Syrian state.”

Lavrov spoke after Tillerson said the American presence in Syria will extend beyond the defeat of the Islamic State as a land-holding terrorist group. U.S. officials maintain that ISIS and al Qaeda fighters remain a threat to the country and can only be defeated by stabilizing Syria and allowing for a political transition that will end the country’s civil war.

“It is crucial to our national defense to maintain a military and diplomatic presence in Syria, to help bring an end to that conflict and assist the Syrian people as they chart a course to achieve a new political future,” Tillerson said Thursday.

Russia, which has provided critical support to Assad, maintains the U.S. has no legitimate role to play in Syria because Assad has not invited American forces to intervene in the country. Lavrov is particularly worried about American efforts to arm local forces in territory liberated from ISIS.

“The U.S. are trying to form alternative bodies of authority on the vast parts of the Syrian territory,” he said through a United Nations translator. “That is a fact, and that does contradict their own obligations.”

That’s a reference to U.S. support for the Syrian Democratic Forces, which partnered to recapture cities held by ISIS and now receives support and training to maintain stability. The arrangement has angered Turkey, a key NATO ally that has long resented American cooperation with the SDF, which is largely composed of Syrian Kurds.

Turks say the SDF has ties to a group of Turkish Kurds that have been branded a terrorist organization for fighting a separatist war against the Turkish central government.

A senior State Department official defended the arrangement earlier Friday.

“Rather, these are elements drawn from all of the ethnic communities in northern Syria, not just the Kurds, to achieve, to help facilitate basic local security which is a key element of stabilization,” the official told reporters on a conference call. “We believe what we are doing shouldn’t be seen as challenging or threatening. It is not a reconstruction or a sustainment of those heavy forces required to fight house by house in [the former ISIS capital city of] Raqqa.”

But Lavrov said that the U.S. shouldn’t be trusted. “This incoherence and lack of a principled commitment to what we negotiate is very typical for the current American diplomacy, including the reasons [for] Americans staying in Syria and the reasons for the U.S. coalition's actions,” he said.