President Assad is reportedly settling his bills for Russian arms orders through that country’s banking system to try to shore up ties with his most powerful ally. The payments, which have increased in recent months, show how Assad has sustained his ties with his main diplomatic defender. The relationship has deepened in recent months. Although it was not possible to say for certain if they are bringing weapons, the number of ships travelling to Syria from a Ukrainian port used by Russia’s arms export monopoly has increased since April.

A Russian defence industry source said Assad had started in recent months paying off a nearly $1bn contract for four S-300 anti-aircraft missile systems and another $550m order for 36 Yak-130 trainer fighter planes.

Another Russian source with links to two Moscow-based members of the Syrian opposition said the Assad family’s financial affairs in Russia have been looked after by the President’s uncle Mohammad Makhlouf, from a hotel room in Moscow. “That’s where Makhlouf meets with those bringing money in. He is looking after all the operations, making sure everything goes according to plan,” said a Syrian opposition member in Moscow.

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Fyodor Lukyanov, editor of the magazine Russia in Global Affairs, said the payments for arms were an important way for Syria to prove to Moscow that it deserves its continued support.

“Syria needs Russia to lend it some international credence and any payments would be a way of ensuring Moscow that it can be taken seriously as a partner,” he said.

Russian weapons accounted for half of Syria’s arms imports before the uprising against Assad began in 2011. Payments for those arms were usually deposited in the state bank accounts of Rosoboronexport, Russia’s state arms dealer. In 2011, when protests against Assad began, Russia sent almost $1bn in arms to Syria’s troops.