Russia is expected to deliver air defense systems, reconditioned helicopters and fighter jets to Syria this year worth nearly half a billion dollars despite international pressure to halt arms sales to Damascus, a defense think-tank said June 26.

The report, by CAST, a Moscow-based think tank, is likely to fuel concerns that Russia is supplying President Bashar al-Assad with arms that are being used against protesters taking part in an uprising against him and air defense systems that could be deployed in the event of international military intervention.

Obtained by Reuters before publication, the report shows a series of contracts that were signed between 2005 and 2007 are at the heart of Russia’s arms sales to Syria, which has been rocked by a vicious cycle of violence for the last 16 months.

The deals were signed long before the start of the rebellion in Syria and after Moscow wrote off some 70% of Syria’s $13.4 billion debt to Russia and the former Soviet Union, a stumbling block that froze Moscow’s arms cooperation with Damascus throughout the 1990s.

Russia is expected to start delivering 12 top-of-the-line MiG-29 fighter jets this year and to deliver a batch of repaired Mi-25 attack helicopters, the report said.

It said air defense systems expected to be delivered to Syria this year included the Buk-M2E, which Moscow began delivering in 2010, and Pantsir-S1 armoured rocket complexes, which are designed to help protect troops against air attacks.

President Vladimir Putin has said the arms that Russia delivers cannot be used in civil conflicts and Foreign Minister Sergei Lavrov has said the supplies are defensive weapons sold in contracts signed long ago.

But U.S. Secretary of State Hillary Clinton has said that Russian statements that the weapons are unrelated to the violence inside the country are “patently untrue.”

The capabilities of Syria’s air defense systems, which are almost completely supplied by Russian manufacturers, are in focus following its shooting down of a Turkish jet last week, an act that increased regional tensions.