The Iranian foreign ministry noted its role in neighbouring Iraq supporting the government against the Islamic State jihadist group independently of a US-led coalition as well as its backing for the Syrian regime against jihadists and other rebels, some of them backed by Saudi Arabia.
Washington "turns a blind eye to the broad political and financial support by Saudi Arabia and its other allies to this ominous phenomenon in the world," foreign ministry spokesman Hossein Jaber Ansari told the official IRNA news agency.
Ansari said Washington's support for Israel despite its decades-old occupation of the Palestinian territories made it the "biggest sponsor of state terrorism".
In its latest annual report published on Thursday, the US State Department said Iran had boosted its support for Palestinian militant groups in Gaza last year, as well as Lebanese Shiite group Hezbollah which has deployed thousands of fighters to Syria in support of President Bashar al-Assad.
Kataib Hezbollah is one of a number of Iran-backed Shiite militias in Iraq that have played a major part in the government's fightback against the Sunni extremists of IS.