The S-300 would help Tehran fend off any Israeli or U.S. air strike against its nuclear facilities. Analysts believe a purchase of the system by the Iranians could accelerate the countdown to military action designed to deny them the bomb.
Israeli defence sources said last July that Iran was set to take delivery of the S-300 by year's end, and possibly as soon as September -- assessments not supported by the United States, which has led a diplomatic drive to rein in Iran's atomic plans.
Iran's Defence Ministry, which already has Russian TOR-M1 anti-aircraft missiles, said in December the S-300 was on order. On Sept 1, Iran's Foreign Ministry said there was no such order.
'We know that, as of now, nothing has been shipped,' an Israeli defence source said on Sunday. 'There seems to be some kind of hold-up. The Russians and Iranians are discussing this, but we have also been speaking to Russia about our concerns.'
Israeli Prime Minister Ehud Olmert flies to Moscow on Monday for talks in which he is expected to ask Russia to curb defence sales to Iran and Syria, another of the Jewish state's enemies.
Russia has denied intending to sell Iran the S-300, the best version of which can track 100 targets and fire on planes 120 km (75 miles) away. The system is known in the West as the SA-20.
A second Israeli source who has access to intelligence briefings said Iran appeared to be vacillating on whether to buy the newest version of the S-300 or a less advanced model.
'Delivery schedule will greatly depend on which version they eventually settle on. If the new one, then it's years away. The other version is readily available,' the source said.
Neither source agreed to be identified given the sensitivity of the subject. Olmert told his cabinet that his Moscow visit would address 'both the supply of weapons to irresponsible elements, the actions of which greatly disturb us, and the Iranian problem, in which Russia has special weight'.
Israel, which is believed to have the Middle East's only atomic arsenal, describes Iran's nuclear programme as a potential threat to its existence.
Iran says its nuclear work is a peaceful project to generate electricity, but has stirred war fears by predicting the Jewish state's destruction.
Like Israel, the United States has alluded to military force as an option against Iran. Yet the allies have often differed on when Iran's uranium enrichment plants might yield enough fissile material for warheads. Israel's timeline is routinely shorter.
(Editing by Dominic Evans) Keywords: IRAN ISRAEL/S 300 tf.TFN-Europe_newsdesk@thomson.com vjt COPYRIGHT Copyright Thomson Financial News Limited 2008. All rights reserved. The copying, republication or redistribution of Thomson Financial News Content, including by framing or similar means, is expressly prohibited without the prior written consent of Thomson Financial News.