Iran has agreed to supply Damascus with $3.6 billion in oil sector in exchange for the right to invest in the country.

Iran has agreed to supply Damascus with $3.6 billion in oil sector in exchange for the right to invest in the country, Syria's state news agency SANA said on Tuesday.

"An agreement was signed (on Monday) in Tehran... by the Iranian and Syrian central banks, granting Syria a credit line worth $3.6 billion," it reported.

The deal stipulates that Syria will pay back the cost of the oil loan "through Iranian investments of various kinds in Syria", said SANA.

Iran is the main regional backer of Syrian President Bashar al-Assad, whose regime has fought for more than 28 months to crush a violent protest movement that morphed into a bloody insurgency.

Oil production in Syria has crashed over the course of the country's war.

Syria was hit by the violent unrest since mid-March 2011, where the Syrian government accuses foreign actors of orchestrating the conflict by supporting the militant opposition groups with arms and money.