Russian Foreign Minister Sergei Lavrov said that U.S. military aid to Syrian rebels may lead to further escalation of violence in the country, according to RIA Novosti.

Lavrov had a phone conversation with U.S. Secretary of State John Kerry on Friday, June 14. The two top diplomats discussed “situation in Syria in the context of Washington’s plans to render military aid to the Syrian opposition,” the foreign ministry said.

“Lavrov stressed that such a move could further escalate tensions in the region, while the U.S. accusations of chemical weapons use by Damascus are not supported by reliable facts,” the ministry said.

The U.S. announced Thursday it will provide military support to the Syrian rebels after it confirms the evidence Syrian government forces have used nerve gas against rebel groups. The Syrian government denied the accusations.