Russia is accusing three Turkish organizations of supplying military equipment to the Islamic State extremist group in Syria.
In a letter to the UN Security Council released on April 1, Russia's ambassador to the United Nations, Vitaly Churkin, claimed that $1.9 million worth of explosives and chemicals were smuggled across Turkey's border to extremist groups in Syria.
"The main supplier of weapons and military equipment to [Islamic State] fighters is Turkey, which is doing so through non-governmental organizations," Churkin wrote in the letter dated March 18.
Churkin said convoys of "various supplies" had been sent to armed groups in Syria by the Besar foundation, the Iyilikder foundation, and the Foundation for Human Rights and Freedoms.
The Russian diplomat claimed that the transfers are overseen by Turkey's National Intelligence Organization.
There was no immediate comment by Turkey's UN mission.
Turkey has backed opponents of Syria's President Bashar Al-Assad, Moscow's ally.
Relations between Russia and Turkey plummeted after Turkey shot down a Russian warplane in November.