US officials said Monday that they want answers from Russia about whether it is selling advanced surface-to-air missiles to Iran, which the United States insists could threaten American troops in Iraq and Afghanistan. A senior military intelligence official said that while Moscow has sent out conflicting responses to reports on sales of long-range S-300 missiles, the United States believes they are occurring. It appears, however, that no equipment has been delivered to Iran, said the official, who spoke on condition of anonymity because of the sensitivity of the matter. Russia's state arms export agency said Monday it is supplying Iran with defensive weapons, including surface-to-air missiles, but did not say whether they include sophisticated long-range S-300 missiles. State Department spokesman Robert Wood said the United States is seeking clarification from Russia. "We have repeatedly made clear at senior levels of the Russian government that we would strongly oppose the sale of the S-300," said Wood. "As the US government has said before, this is not the time for business as usual with the Iranian government." Meanwhile, Russia's state arms export agency said Monday it is supplying Iran with defensive weapons, including surface-to-air missiles, but did not say whether they include S-300 missiles. Iranian media reported Sunday that Russia had begun supplying the S-300s - an action Israel and the United States have aggressively opposed. Rosoboronexport said in a statement that "only weapons of a defensive nature are being supplied to Iran, including anti-aircraft weaponry." It added that, previously, Tor-M1 air-defense systems were supplied to Iran. "Russia is developing military-technical cooperation with Iran in strict compliance with its international commitments stemming from nonproliferation agreements. This cooperation cannot be a source of concern for third countries," the statement said. Rosoboronexport spokesman Vyacheslav Davydenko confirmed that S-300 missiles were considered defensive, but refused to say whether they were being supplied to Teheran. Israel and the United States fear that, were Iran to possess S-300 missiles, it would use them to protect its first nuclear power plant now under construction at Bushehr by Russian contractors. That would make any potential military strike on the plant much more difficult. The Interfax news agency later quoted an unnamed Russian military official as saying S-300 missiles would be delivered to Iran soon from Russian Defense Ministry warehouses. "The S-300 systems are now being prepared for transfer to Rosoboronexport and their further shipment to the customer," Interfax quoted the official as saying. A Russian Defense Ministry spokesman could not be reached for comment. Israel, the United States and much of the international community believe that Iran is secretly developing nuclear weapons. Teheran insists its uranium enrichment program is intended solely for civilian energy needs. Bushehr is scheduled to go online early in 2009 after repeated delays. In Israel, Foreign Ministry spokesman Yigal Palmor said Israeli officials asked Moscow on Sunday about the Iranian media report on the S-300 deliveries. "We were reassured that the report was groundless. We were told that Russia is keeping their promise to [Prime Minister] Ehud Olmert that Russia wouldn't do anything to jeopardize Israel's security," Palmor told The Associated Press. "That is the commitment they have taken and the Russians say this report is groundless."