Alexander Losyukov made the statement in response to journalists' request for a comment over Iran's announcement that Russia would supply advanced S-300 air defense missile systems to the Islamic Republic.
"I know we are assisting in work to reinforce Iran's air defense systems," Losyukov said.
But the official declined to elaborate: "I have no concrete information on the issue and can make no comment whatsoever on the type of [military] hardware," he said.
Iran's Fars news agency on Wednesday quoted the country's Defense Minister Mostafa Mohammad Najjar as saying Tehran signed a contract with Russia Tuesday for the delivery of advanced S-300 air defense missile systems to the Islamic Republic. The minister provided no details of the deal or any timeline for delivery of the system.
The signing of the deal follows last week's session of the Russian-Iranian commission on military-technical cooperation in Tehran, where the sides reviewed existing agreements and discussed further steps for increasing cooperation in the military sphere.
The advanced version of the S-300 missile system, called S-300PMU1 (SA-20 Gargoyle), has a range of over 150 kilometers (about 100 miles) and can intercept ballistic missiles and aircraft at low and high altitudes, making this system an effective tool for warding off possible air strikes on Iran.
U.S. authorities have repeatedly called on Russia to stop arms deliveries to countries whose political regimes Washington disapproves of, including Iran.
However, Russian President Vladimir Putin said in October that Russia would not take into consideration attempts to impose arms deal restrictions "based on unilateral and politicized assessments". He said deliveries of Russian weapons were aimed exclusively at increasing the defense capability of the countries receiving them, and at maintaining their stability.
Moscow earlier supplied Iran with 29 Tor-M1 air defense missile systems under a $700-million contract signed in late 2005. Russia has also trained Iranian Tor-M1 specialists, including radar operators and crew commanders.