MOSCOW - Iran's decision to sue in the International Court of Justice over Russia's refusal to sell S-300 air defense systems to Tehran surprised Moscow, the Foreign Ministry said Thursday.

"Judging from the traditionally friendly bilateral relations this is surprising that our Iranian partners opted for such a way," Foreign Ministry spokesman Alexander Lukashevich told the Interfax news agency.

Mahmoud Reza Sajjadi, the Iranian ambassador to Moscow, said Wednesday that Tehran filed suit against Russia in the International Court for Moscow's refusal to supply Iran with the missile defense systems.

Lukashevich suggested that Iran try to solve the dispute by direct dialogue, stressing that Moscow acted in accordance with United Nations resolutions.

"Russia was unable to fulfill the corresponding contract in connection with the UN Security Council's resolution 1929 and Russian President's decree 1154 of September 22, 2010," Lukashevich said.

Sajjadi, meanwhile, insisted that the S-300 shipment does not fall under the resolution, which prohibits the sale of conventional weapons, including missiles, tanks, military helicopters, warplanes and warships, to Iran.

Iran and Russia signed a contract for the S-300 system in 2007. In September 2010 Russian President Dmitry Medvedev signed a decree banning shipments to Iran of the weapons and equipment listed in the UNresolution.