It has been reported that Moscow's decision to halt delivery of powerful S-300 air-defense missiles to Iran, citing the new U. N. sanctions on the Islamic Republic, may be politically convenient but it could carry a hefty cost for Russia in the Middle East.

Largely because of U. S. and Israeli pressure, the Kremlin has been delaying delivery of five S-300PMU batteries under a $700 million contract in 2007.

But Russian leaders have now found a valid excuse to deny the Islamic Republic the weapons it wants to protect its nuclear facilities from attack.

It was also noted by the reports that may have earned Moscow brownie points in Washington but there is no doubt a quid pro quo involved somewhere in going along with the sanctions proposed by the Americans and their European allies.

Just what that might be isn't clear but there could well be a downside for the Russians and the arms industry they are striving to bolster as a means of restoring some of Moscow's influence in the Middle East as U. S. power is seen to be ebbing.

It will be difficult for Iran to replace Russia as an arms supplier but it's likely to retaliate, one way or another.

Including those who were Cold War clients of the Soviets, the Arab states have learned over the years that Moscow isn't the most reliable of arms suppliers.

That category included Syria, Algeria, Egypt, Yemen and Libya at various times.

Apart from the fact that its weapons systems have long been considered inferior to those produced by the Americans and to a lesser extent the British, French and Italians, deliveries have often been erratic. (With Inputs from Agencies)