In a first, Iran has allowed Russia to use one of its bases to stage and take off for attacks inside Syria — something unheard of in modern times in the Islamic Republic.

Iran's constitution, ratified after its 1979 Islamic Revolution, bans the establishment of any foreign military base in the country. However, nothing bars Iranian officials from allowing foreign countries to use an airfield.

Russia has never used the territory of another country in the Middle East for its operations inside Syria, where it has been carrying out an aerial campaign in support of President Bashar al-Assad's government for nearly a year.

The announcement suggests co-operation on the highest levels between Moscow and Tehran, both key allies of the embattled president.

In Tehran, the state-run IRNA news agency quoted Ali Shamkhani, the secretary of Iran's Supreme National Security Council, as saying on Tuesday that Tehran and Moscow have exchanged "capacity and possibilities" in the fight against the Islamic State group.

Shamkhahi says: "With constructive and extended co-operation between Iran, Russia and Syria and the resistance front [Hezbollah], the situation has become very tough for terrorists and the trend will continue until the complete destruction of them.