"The Russian Federation implements and plans to further implement the military-technical cooperation with the Islamic Republic of Iran in strict accordance with existing legislation and its international obligations," Russia's Federal Service for Military and Technical Cooperation said.
The service released a rare statement after the Interfax agency, citing a Russian government source, reported ealier this week that Iran had not yet paid Russia for the S-300 anti-aircraft missiles.
The source said no payments had been made because Russia's government has not given its final approval for the sale of S-300 missiles to Iran.
"We can't give comments regarding concrete plans or obligations with regards to existing contracts as it would mean becoming an unreliable partner (and) give potential competitors a chance to take advantage of the situation," the military service said.
Thursday's statement is likely to fuel further unease in the West over Russia's cooperation with Iran. Russia has so far refused to discuss tougher sanctions against Tehran, which the West suspects of seeking to obtain nuclear weapons.
