US officials said that they want answers from Russia on whether it is selling advanced surface-to-air missiles to Iran. The US insists such a move could threaten American troops in Iraq and Afghanistan. A senior military intelligence official said Monday that the US believes the sale of Russian long-range S-300 missiles is taking place. However, the official said it appears that no equipment has yet been delivered to Iran. The official 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. State Department spokesman Robert Wood said the US is seeking clarification from Russia.