The Bulgarian authorities have been informed that the Syria-bound Russian cargo aircraft seeking clearance to overfly Bulgaria’s territory could have possibly been transporting weapons, Defence Minister Nikolay Nenchev said on Tuesday.

“We denied permission. We are a sovereign state”, Nenchev said on bTV station, commenting on the Foreign Ministry’s decision to reject a request by Moscow to permit Russian military transport aircraft said to be carrying humanitarian aid to Syria to cross Bulgaria’s airspace.

Asked whether the Bulgarian authorities had been tipped by intelligence agencies about potential transportation of weapons from Russia to Syria by Russian aircraft Nenchev replied: “Quite possible, by domestic as well as foreign agencies”.

The Foreign Ministry in Sofia said earlier on Tuesday that it had refused to allow Russian cargo planes to overfly Bulgaria en route to Syria due to “incorrect information in the requests … regarding the purpose of the flights and the cargo.”

Media reports have led to speculation that Russia is stepping up its military support for Syrian President Bashar al-Assad's government.