WASHINGTON – U.S. officials said Monday that they want answers from Russia on whether it is selling advanced surface-to-air missiles to Iran, a move the U.S. 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 the sale of long-range S-300 missiles, the U.S. believes it is taking place. However, it appears that no equipment has yet 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 U.S. 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," Wood said. "As the U.S. government has said before, this is not the time for business as usual with the Iranian government."

Iran currently has an antiquated missile defense system, dating back to the 1960s and 1970s, so the Russian sale would provide Tehran a much longer range, more mobile and lethal capability. With a range of roughly 75 miles, the Russian system would allow Iran to reach coalition forces operating in Iraq and Afghanistan, if the missiles were moved near the borders.

Both the U.S. and Israel have strongly opposed the sale, saying that supplying such an advanced anti-aircraft system to Iran would shift the military balance of power in the Middle East. It also would make any strike at Iran's first nuclear power plant — which Russia is helping to build — more difficult.

There have been indications that Russia intends to supply only defensive weapons to Iran, thus keeping in line with U.N. Security Council resolutions that impose sanctions on Iran for refusing to halt its uranium enrichment and prohibit supplying Iran with materials that could contribute to its nuclear program.

Officials acknowledge that the sale of the S-300 system is not prohibited by the resolution.

Israel and the United States fear that Iran could use the S-300 missiles to protect its uranium enrichment plant at Natanz or the country's first atomic power plant now under construction at Bushehr by Russian contractors.

The U.S. and other nations believe Iran is secretly developing nuclear weapons, but Iran insists its uranium enrichment program is intended solely for civilian energy needs.

While the possibility that the U.S. might launch an attack against Iran's nuclear facilities faded about a year ago, Israel has never ruled out a strike of its own, and is considered the nation most likely to take action.

Iran's president has said that Israel should be "wiped off the map."

The sale of S-300 missiles, said the military intelligence official, presents a decision point for Israel, since once the anti-aircraft system is in place it could deter any strike.