Bulgaria has closed the country's airspace to Syrian-bound Russian flights.
Bulgarian authorities have not given any reason for refusal to provide an airspace to two Russian flights.
The planes will have to take an alternate route over Iran.
Russian Federation has submitted a request to Bulgarian authorities to provide airspace to two Russian flights to deliver humanitarian aid to Syria.
Bulgarian authorities have refused to provide an airspace without giving an official reason.
On Monday, September 7th, Greece also informed of the request of USA to close their airspace to Russian Syria-bound flights.
Russia has been accused of building up its military presence in Syria.
Russia is a long-time ally of Syrian President Bashar al-Assad, whose rule the United States and other western powers favor ending via a political transition.