The U.S. says the number of global terrorist attacks declined slightly between 2014 and 2015. Yet the Islamic State expanded its reach, and Iran remained the leading state sponsor of terrorism even as it sealed a nuclear deal with world powers.

In its annual survey of terrorism released Thursday, the State Department reported a 13 percent decrease in attacks in 2015 but says the threat from extremists continues to evolve as groups exploit lawlessness in ungoverned areas.

The report says that while the Islamic State's control of territory in Iraq and Syria ebbed in 2015, its followers carried out deadly attacks in Turkey, France and Lebanon, demonstrating international capability. It says Al-Qaida and affiliates also remained active in Afghanistan, Pakistan and parts of Africa.