Moscow has delayed the delivery of advanced air defence missiles to Iran, Russian officials said Wednesday, in the latest sign of strained ties between Moscow and Tehran.

The announcement of the delay in the controversial contract to sell S-300 missiles to Iran came a day after Israeli Prime Minister Benjamin Netanyahu visited Moscow in a bid to add new pressure on Iran.

"The delay is due to technical problems. The delivery will be carried out when they are resolved," Alexander Fomin, deputy head of Russia's Federal Service for Military-Technical Cooperation, told Interfax news agency.

Fomin, whose service oversees Russian arms exports, made the comments while attending a defence exhibition in New Delhi. He did not clarify what the problems were or how long it would take to fix them.

The engineer in charge of building the S-300s said there were nothing wrong with the missiles and called the delay a political decision.

"There are no technical problems with the S-300 systems. This is a political issue," Vladimir Kasparyants, head constructor of air defence systems at Almaz-Antey, the company that builds the S-300, told Interfax.

Russia's S-300 contract with Iran has raised hackles in the United States and Israel, which believe that Tehran could use the missiles to defend its nuclear facilities against attack.

Western powers suspect that Iran is seeking to build an atomic bomb under the guise of its civilian nuclear energy programme, although Tehran says the programme is peaceful in nature.

Neither the United States nor Israel have ruled out air strikes in order to prevent Iran from acquiring nuclear weapons. Analysts say that S-300s could greatly complicate such air strikes.

Russia has shown growing impatience with Iran as tensions have mounted in the standoff over Tehran's nuclear programme, after years in which the two countries enjoyed friendly ties.

On Tuesday, Russia joined the United States and France in criticising a new push by Iran to step up uranium enrichment, and Moscow said it could not exclude a new round of sanctions against Iran.

Russian Prime Minister Vladimir Putin met Tuesday with Netanyahu, the prime minister of Iran's arch-foe Israel.

Netanyahu came to Moscow seeking to win the Kremlin's support for "biting sanctions" against Iran, and he has also been outspoken in his criticism of Russia's S-300 sale to the Islamic Republic.

Russia has been secretive about the missile contract, but Interfax has reported that it calls for Moscow to sell Tehran five batteries of S-300PMU1 missiles for 800 million dollars (530 million euros).

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

Iran has expressed frustration with the delay in the missile delivery, and last week a top Iranian military commander said Tehran would build its own air defence missiles that would be even better than the S-300s.

Separately, Iran announced on Wednesday that it had arrested two Russian nationals last week on the anniversary of its 1979 Islamic revolution and that one of them would face charges.

One of the Russians "was arrested for illegal entry into the country and referred to the judiciary" while the other was released, Tehran's prosecutor Abbas Jafari Dolarabadi told ISNA news agency.