WASHINGTON — Terrorist violence exploded around the world last year, driven by a surge in attacks by the Islamic State extremist group in the Middle East and Boko Haram in West Africa, the State Department said in a report Friday.

The number of terrorist attacks jumped 35 percent, to 13,500, while the number of fatalities soared 81 percent, to 33,000, the report says. A major factor was an increase in especially deadly attacks, including 20 assaults that killed 100 or more people.

The surge in lethality comes as governments have collapsed or come under attack in parts of the Middle East and Africa, including in Syria, Iraq, Yemen, Libya and Nigeria.

The number of people kidnapped or taken hostage tripled, to more than 9,400, largely at the hands of Islamic State and Al Nusra Front in Syria and Boko Haram in Nigeria.

Tina Kaidanow, the State Department’s counterterrorism coordinator, said much of the terrorist violence was confined to a few troubled nations.

But she said the threat of “lone wolf attacks” is growing in the West, in part because Western governments are making it harder for recruits to travel to join extremist groups abroad. Still, an estimated 16,000 foreign fighters joined Islamic State in Syria and Iraq in 2014.

The extremist groups’ effective outreach on social media and the Internet is also driving zealots to plot and launch attacks, Kaidanow said, citing lethal assaults carried out last year by gunmen in Ottawa and Sydney.