Foreign Ministry spokesman Mohammad Ali Hosseini said the U.S. comments were "baseless."
The reaction comes a day after U.S. Assistant Secretary of State for South and Central Asian Affairs Richard Boucher said there has been "a series of indicators" that Iran is getting involved in "a more unhealthy way" in Afghanistan.
Earlier this week, U.S. General Peter Pace, the chairman of the Joint Chiefs of Staff, said coalition forces had intercepted Iranian-made mortars and explosives in Afghanistan's Kandahar Province, heading to the Taliban.
Pace and Boucher have said it is unclear exactly who was providing the weapons.
Kabul Mulls Relations Iran
Afghanistan has recently been preoccupied with its relations with Pakistan. But increasingly, ties with Tehran are coming to the fore. more
Between Washington And Tehran
Afghan Foreign Minister Rangin Dadfar Spanta told RFE/RL in May 2006 that his country could help improve relations between Iran and the United States. more