Increased Foreign arms supply to Syria

Mr Lavrov claimed in a speech to Russia's lower house of parliament last week that Russian weapons sent to Syria were for "external threats" and have not been used against civilians or peaceful demonstrators. However, Human Rights Watch believes Russian-made mines were laid on Syria's borders with Turkey and Lebanon, posing danger to fleeing refugees.

Nearly $1bn worth of Russian missiles and aircraft upgrades were reportedly sold to Syria in 2011, while shipments of smaller weapons have been harder to trace.

A Russian-operated ship carrying bullets was halted during a refuelling stop in Cyprus in January and gave reassurances it was not travelling to Syria. However, after being released the ship dropped off tracking systems and sailed to the Syrian port of Tartus.

Some orders, including 24 MiG combat aircraft and 36 Yak-130 trainer/combat aircraft, have yet to be delivered. Experts from SIPRI said these would improve the capability of Syrian government forces to hit rebel positions.

Russia is keen to preserve long-standing political and business ties with Syria and its only naval base outside the former Soviet Union is situated in Syria's Mediterranean port of Tartus.

The Kremlin has defended the flow of arms, stressing that it wants to prevent an outside intervention in Syria like the one in Libya where, it says, Nato countries used a UN resolution as a cloak for supporting rebels against Muammar Gaddafi.

Moscow's support for Mr Assad has prompted hand-wringing in Washington.

Earlier this month, a group of 17 senators called on the Department of Defence to cancel a $900m purchase of 21 Russian helicopters for use in Afghanistan. "U.S. taxpayers should not be put in a position where they are indirectly subsidising the mass murder of Syrian civilians," the senators said.

Despite calling on Mr Assad to step down, Western and Arab powers have hesitated to supply weapons to the lightly-armed rebel force, the Free Syrian Army, fearing the conflict could spread. The EU imposed an arms embargo on Syria last year.