The agreement was signed in Damascus on August 26, 2015, more than a month before Russia launched a campaign against the Islamic State in Iraq and the Levant (ISIL or Daesh) group and other terrorists at the request of Syria's President Bashar al-Assad, the AFP reported.
The Russian government on Thursday released the text of the agreement, which said that it had been "concluded for an open-ended period of time."
Under the agreement, the Russian air group and its infrastructure will be deployed at Hmeymim air base in Syria free of charge.
The air group flies on combat missions on order from its commander according to the flight schedule agreed with Syria. Russia and Syria also agree on the Russian air group’s structure, according to a Tass report.
The agreement said that Russia could bring any weapons, ammunitions and other materials necessary for the air group into Syria free of fees or duties.
All the property installed at the airfield and temporary deployed infrastructure facilities are considered to be the property of Russia.
The personnel can cross the border on papers that are valid for exit from Russia and are not subject to inspection in Syria.
The deal was made to defend the "sovereignty, territorial integrity and security of the Russian Federation and the Syrian Arab Republic," according to the document.
"The presence of the Russian air group in the Syrian territory is designed to maintain peace and stability in the region. Its purpose is purely defensive is defensive and is not directed against any other state," the treaty’s preamble said.
Since late September, Russia has been carrying out bombings against the Daesh terrorist group in Syria, after Russia's parliament granted President Putin authorization to deploy the country's air force abroad.