Deaths from terrorism rose 61 percent between 2012 and 2013, according to the Global Terrorism Index 2014 report.
Ten thousand attacks killed nearly 18,000 people in 2013.
The groups responsible for the most attacks were the Islamic State, al Qaeda, Boko Haram, and the Taliban, the BBC reports. All of those groups used "religious ideologies based on extreme interpretations of Wahhabi Islam," according to the report.
Terrorism affected Iraq more than any other country, but Afghanistan, Pakistan, Nigeria, and Syria were also deeply affected. The five countries accounted for 80 percent of terrorism deaths.
"Not only is the intensity of terrorism increasing, its breadth is increasing as well," it notes.
Steve Killelea, IEP executive chairman, told the BBC the latest increase in deaths from terrorism was primarily due to the civil war in Syria, which began in 2011.
"The destabilisation in Syria, which has now overflowed into Iraq, is where we feel the upsurge in terrorism," Mr Killelea said.