MOSCOW: Two Russian ships heading for a naval exercise off Syria this month are picking up munitions to drop at the Syrian port of Tartous, news agencies reported on Thursday.

Russia has been Syrian President Bashar al-Assad's main foreign protector during a 22-month uprising against his rule and is its biggest arms supplier. It leases a naval maintenance and supply facility at Tartous that is its only military base outside the former Soviet Union.

A Russian General Staff source told the Itar-Tass news agency that the landing ship Kaliningrad had docked at the Russian Black Sea port of Novorossiisk to pick up munitions and another landing ship, the Alexander Shabalin, was due there for the same purpose.

It was not clear who the munitions were for, however.

"It's possible that the ships are delivering some kind of munition for the Syrians, (or) it's possible that they are carrying it to the Russian (naval base)," said Andrei Frolov, a naval expert at the Moscow-based military think tank CAST.

"(If it's for the Syrians) it's unlikely to be something new. But it could be some parts for weapons systems. Possibly they are delivering munitions of some sort that were repaired in Russia."

Itar-Tass cited an unnamed military source as saying that the warships would join at least seven others off Syria for what the Defence Ministry has said will be Russia's biggest naval exercise in decades.

Frolov said the scale of the manoeuvres was probably intended to underline Russia's interest in Syria, where it has repeatedly argued against outside intervention.

Russia, which has blocked three U.N. Security Council resolutions aimed at pressuring Assad to end the violence from forces loyal to him, delivered nearly $1 billion in arms to Syria in 2011. CAST said it had been due to send half a billion dollars' worth last year.

A source close to Rosoboronexport, Russia's arms export monopoly, said Russia had signed no new contracts with Syria in 2012, but Moscow has defended its fulfiment of existing contracts.

Last summer, the United States criticised an attempted Russian delivery of repaired helicopters, and Secretary of State Hillary Clinton called Russia's claims that its deliveries were unrelated to domestic violence "patently untrue".

The ship carrying the helicopters turned back when a British insurer cancelled its cover after being informed that the ship was carrying weapons. Russia promised to deliver the helicopters after reflagging the vessel.