The United States is concerned about the potential sale of Russian S-300 missile defense systems to Iran, but remains confident in its military capabilities.
US Defense Department Spokesman Peter Cook said in a press briefing on Tuesday: "We have long expressed our concerns over reports on this possible sale...but this is something we have been tracking and in general, we are confident in our capabilities, even if that system is sold."
On Sunday, Iran's Defense Minister Hossein Dehghan said the country could receive S-300s from Russia by the end of 2015.
Russia and Iran signed an $800-million deal for delivery of five S-300 battalions in 2007, but the deal was suspended after the UN Security Council issued an arms embargo on Tehran amid suspicions that it was trying to facilitate nuclear weapons development.
On April 13, Russian President Vladimir Putin signed a decree lifting the ban on the sales, which do not violate the embargo.
The United States has expressed concern over Moscow's announcement arguing the sale would create instability in the Middle East.