In 2007, Russia and Iran signed an $800-million deal for the delivery of five S-300 battalions.
In 2011, Iran sued Russia's state arms exporter Rosoboronexport in the Geneva Arbitration Court after Moscow suspended the contract for delivery of five S-300 systems, citing the UN Security Council-imposed arms embargo against Tehran.
"For this [a decision regarding deliveries of S-300], a key requirement is the withdrawal of a lawsuit. They have not withdrawn it yet, we are waiting. We cannot [simultaneously] take part in legal proceedings over one contract and implement deliveries on the other," the source said.
Last week, Russia and Iran signed a memorandum on the implementation of the agreement for the delivery of the missile defense systems.
Earlier this month, an Iranian defense source told Sputnik that Tehran expected to receive the Russian S-300 missile defense systems 30-40 days after the signing of the new deal with Moscow. According to the source, Iran will withdraw its lawsuit against Russia immediately after the signing of a new agreement on S-300 deliveries.