The Obama administration is accusing Iran of increasing support for global terrorism to levels not seen for two decades.
The administration also says core elements of al Qaida in Afghanistan and Pakistan are heading for defeat, as their leaders increasingly fight for survival.
State Department officials released Country Reports on Terrorism for 2012 on Thursday.
The reports say Iran's sponsorship of terror has reached a tempo unseen since the 1990s, with attacks plotted in Africa, Europe and south-east Asia.
Those include an attack on a bus carrying Israeli tourists in Bulgaria that killed six as well as thwarted strikes in India, Thailand, Georgia and Kenya.
The reports say core al Qaida continues to weaken.
But they also note the US must defend itself from a "more decentralised and geographically dispersed terrorist threat".