The U.S. has accused Iran and Syria of backing the insurgency and unrest in Iraq and Lebanon, and suspects the Islamic Republic of pursuing a secret nuclear weapons program.
U.S. Defense Secretary Robert Gates said the United States has credible evidence of Iran's military and technical aid to Shiite militias.
Mohammad Ali Hosseini, the official spokesman for the Iranian Foreign Ministry, said the U.S. has "good experience in fabricating evidence" and called the accusations groundless and inadmissible.
High-ranking U.S. officers claim that more than 170 American servicemen have been killed by Iranian-made bombs in Iraq since June 2004, and that the bombs are powerful enough to destroy Abrams tanks.
Tensions between Tehran and Washington are high over the U.S.-led campaign in Iraq and the country's policies in the Middle East at large, as well as over Iran's controversial nuclear program.
In response to Iran's perceived involvement in Iraq, U.S. President George W. Bush authorized American troops to kill or capture Iranian agents suspected of abetting the insurgency there.
