The development of Russia's formidable S-500 air defense system is lagging behind schedule by at least two years, the Izvestia daily said on Wednesday citing a defense industry source.

According to the source, the first prototypes will be ready and tested by 2015, while the deliveries to the Russian army could start in 2017 at the earliest.

"The production cycle of this system is about two years. Therefore, even if the prototypes are ready by 2015, the military will not receive production models earlier than in 2017," the source said.

A source in the Russian Defense Ministry confirmed that the earlier announced schedule of S-500 deliveries in 2015 was "too optimistic," as the prototypes should have already been undergoing field tests to meet the deadlines.

The S-500, a long-range air defense missile system, is expected to become the backbone of a unified aerospace defense system being formed in Russia.

The system is expected to have an extended range of up to 600 km (over 370 miles) and simultaneously engage up to 10 targets.

The Russian military has demanded that the system must be capable of intercepting ballistic missiles and hypersonic cruise missiles and plans to order at least ten S-500 battalions for the future Russian Aerospace Defense.