MOSCOW — Moscow is unlikely to deliver a shipment of S-300 anti-aircraft missiles to Syria before the autumn, a Russian arms industry source told Interfax news agency on Friday.

That contrary to insinuations by Syrian President Bashar al-Assad that some of the missile systems had already been delivered.

The source suggested the delivery could be accelerated if neighboring countries carried out air attacks on Syria or if a no-fly zone were to be imposed on the country.

"Regarding the deliveries of the S-300, they can begin no earlier than the autumn. Technically it's possible, but much will depend on how the situation develops in the region and the position of Western countries," said the source, speaking on the condition of anonymity.

Russia has promised to fulfill an order of the long-range surface-to-air missiles to Syria, saying it hopes to deter foreign military intervention in Syria.

The S-300s can intercept manned aircraft and guided missiles and Western experts say their delivery could improve Assad's chances of retaining power.

The head of aircraft maker MiG said separately that Russia was counting on providing Syria with 10 MiG-29 fighter planes and was discussing details with a Syrian delegation, RIA news agency reported.

It did not say when they might be delivered.