Russian media reported on Friday that Russian and Iranian officials had signed contracts in November worth a billion dollars for weapons including up to 30 Tor-M1 missile systems to be delivered over the next two years.
"A contract for the delivery of air defence Tor missile systems to Iran has indeed been signed," Ivanov said in comments broadcast by the state channel Rossiya on Monday.
The defence minister defended the deal, saying the weapons system was purely defensive.
"This is exclusively, 100%, defensive weaponry," he said, pointing out that the missiles could only strike targets in the air. "This unequivocally will not change the balance of forces in the region," the Interfax news agency quoted him as saying.
Nevertheless, US State Department spokesman Adam Ereli said the United States strongly opposed the missile sale, adding that Undersecretary of State Nicholas Burns made the point in talks with Russian officials last week in Moscow.
"We certainly do not feel that this is a sale that would serve the interests of us or the region," said Ereli. "We will continue to pursue this issue with Russia."
The reports of the missile sale rang alarm bells in Israel, which considers Iran its biggest threat.
Israeli concerns were heightened recently when Iranian President Mahmoud Ahmadinejad said Israel should be "wiped off the map".
"This is exclusively, 100%, defensive weaponry"
Russian defence minister
Senior Israeli politicians have ratcheted up the tough talk against Iran, led by former prime minister Benjamin Netanyahu's call for a strike against Iranian nuclear installations.
Netanyahu told the Maariv daily in comments published on Monday that the solution was a pre-emptive strike similar to the 1981 Israeli attack that destroyed an unfinished Iraqi nuclear reactor.
Interfax said the mobile Tor-M1 system could identify up to 48 targets and fire at two targets simultaneously at a height of up to 6100 metres (20,000 feet).
On Saturday, an influential Iranian official downplayed the deal, telling the Islamic Republic News Agency that Iran had been trading arms with many countries and would continue to do so.
The US and Russia are supporting efforts by the European Union to persuade Iran to halt development of nuclear weapons in exchange for economic incentives, such as trade opportunities.
Russia, which has a long and lucrative relationship with Iran, has offered to try to resolve a key dispute by offering to enrich uranium for an Iranian civilian nuclear energy programme as a safeguard against Iran using enrichment for weapons purposes.