Russia has assured Iran it will honour a deal to supply the Islamic Republic with advanced S-300 air-defence missiles, Tehran's ambassador to Moscow said Friday.

"We had heard reports that Russia would not deliver these systems to Iran, but we asked the Russian side and they denied it," Seyed Mahmoud Reza Sajadi told reporters in Moscow.

"The delivery deadline has already passed, but the Russian side has cited technical problems which it is working to fix," he added. "We feel that this question will be resolved in the space of one to two months."

The envoy's comments came after Iranian officials had accused Moscow of violating its contract and succumbing to growing pressure from the United States and Israel to halt delivery of the missile systems.

Russia, Iran's closest ally among major world powers, has never officially confirmed the S-300 contract but has reserved the right to sell arms to Iran as long as they are defensive in nature.

Russia's Interfax news agency has reported that the contract calls for Moscow to sell Tehran five batteries of S-300PMU1 missiles for a total price of around 800 million dollars (530 million euros).

A top Iranian general said this month that Russia was six months late in supplying the missiles.

"The contract for the delivery of the Russian S-300 systems is signed. These are defence weapons, intended particularly for the defence of Bushehr (nuclear power plant) which Russian specialists are building in southern Iran," Sajadi said.

"Neither side plans to go back on this contract.... It is profitable for both sides," the diplomat said.

The S-300PMU1, codenamed the SA-20 Gargoyle by NATO, is a mobile land-based system designed to shoot down aircraft and cruise missiles.

The United States and Israel -- neither of which have ruled out air strikes to prevent the Islamic Republic from acquiring an atomic bomb -- fear Iran could use the systems to boost defences around its nuclear sites.

Iran denies developing atomic weapons and insists that its nuclear energy programme is peaceful in nature.

Russia has largely backed Iran's claims and is building Iran's first nuclear power plant in Bushehr.