DUBAI, United Arab Emirates — Russia will complete the delivery of S-300 air defense systems to Iran by the end of the year, according to a Russian presidential aide for military-technical cooperation.

Speaking to Russian state news agency TASS, Vladimir Kozhin said that one S-300 battalion has already been supplied to Iran. He added that other launchers due under the effective contract would be delivered by the end of 2016.

"The first batch — about one battalion — has been shipped. We will comply with our liabilities by the end of the year," Kozhin told TASS.

The first battalion was shown off by the Iranian military at the National Army Day parade in Tehran on April 17, six days after the receipt of the system.

According to the original contract, Moscow and Tehran signed for the delivery of five battalion sets of S-300 PMU1 air defense missile systems in 2007.

During a brief to the Iranian parliament last month, the head of its defense commission, Esmayeel Kosari, said: "Based on the contract and the agreement inked between Iran and Russia, the missile systems' equipment will be transferred to the country in parts.

"Based on the timetable, the S-300 parts will be sent to Iran in different stages, and its parts, including missiles, launch pads and radars, will be delivered to the country gradually."

Kosari said that the large volume of S-300 parts is the reason behind its gradual delivery to Iran.