Global terror attacks soared by a third in 2014 with an 81 percent spike in the number of deaths, the United States said Friday in a grim annual report.

"The number of terrorist attacks in 2014 increased 35% and total fatalities increased 81% compared to 2013, largely due to activity in Iraq, Afghanistan, and Nigeria," the report says, adding that the war in Syria was a significant factor driving instability.

In total, there were 13,463 attacks in 2014 which killed 32,727 people, up on 9,700 assaults in 2013 in which 17,800 died.