US officials said on Thursday that four of the 26 Russian cruise missiles fired on Wednesday from a Russian ship in the Caspian Sea launched at Syria crashed in Iran.
Russian Defence Ministry spokesman Major General Igor Konashenkov rejected the claim and said the missiles hit their targets in Syria.
The US government source also added that Russia had been using Iranian airspace to send their missiles from Caspian Sea into Syria, hitting rebels fighting Syrian President, Bashar al Assad.
Russia has been claiming that it is fighting against ISIS in Syria since its attacks started on September 30.
Reports from Syrian activists and opposition show that most of the areas hit by Russian air strikes are controlled by opposition groups.
“Russian Air Forces have carried out 55 air strikes against moderate opposition groups out of a total of their 57 air strikes in Syria. They have only carried out two attacks against DAESH according to our military sources,” Turkish Prime Minister Ahmet Davutoglu said on Wednesday.