Deaths from terrorism in OECD countries increased by 650 per cent last year despite a marked fall globally as Islamic State (ISIS) and Boko Haram militants suffered military defeats at home but committed more attacks abroad, a report said on Wednesday.

The Global Terrorism Index (GTI) said worldwide there had been 29,376 deaths caused by terrorism in 2015, a drop of 10 per cent and the first fall in four years, as action against Islamist militants ISIS in Iraq and Boko Haram in Nigeria cut the numbers killed there by a third.

However, the report said the groups had spread their actions to neighbouring states and regions, causing a huge increase in fatalities among OECD (Organisation for Economic Cooperation and Development) members, most of which are wealthy countries such as the United States and European nations.

Signs with the names of some of the 100-plus victims of a double suicide bombing in Ankara blamed on ISIS militants against a pro-Kurdish peace rally are shown in Turkey's capital on Oct. 26, 2015. (Adem Altan/AFP/Getty Images)

It said 21 of the 34 OECD member countries had witnessed at least one attack with most deaths occurring in Turkey and France where coordinated attacks by ISIS gunmen and suicide bombers at the Bataclan music venue, a soccer stadium and several cafes in Paris last November killed 130 people.

Denmark, France, Germany, Sweden and Turkey all suffered their worst death tolls from terrorism in a single year since 2000, according to the index which is produced by the Institute for Economics and Peace (IEP) think-tank.

Economic impact estimated at $89B

In total, 23 countries registered their highest ever number of terrorism deaths.

"While on the one hand the reduction in deaths is positive, the continued intensification of terrorism in some countries and its spread to new ones is a cause for serious concern and underscores the fluid nature of modern terrorist activity," said Steve Killelea, the IEP's executive chairman.

"The attacks in the heartland of western democracies underscore the need for fast-paced and tailored responses to the evolution of these organisations."

The execution of about 300 civilians in Qaim, Iraq by ISIS in spring of 2015 was considered the deadliest incident of the year, with three of the 10 deadliest occurring in Syria. Other notable incidents near the top were the downing of a Metrojet plane bound for Russia in Egypt, and the slaying of over 150 mostly non-Muslim students at Garissa University in Kenya.

The annual index ranks countries based on data from the Global Terrorism Database run by a consortium based at the U.S. University of Maryland.

The remains of a SUV driven by the couple responsible for the Dec. 3, 2015 attack in San Bernardino, Calif., is shown. It was the deadliest terrorist attack in the U.S. in at least six years. (Mario Anzuoni/Reuters)

Iraq, Afghanistan, Nigeria, Pakistan and Syria, which accounted for 72 per cent of all deaths, were the top five ranked countries in the GTI. The United States ranked 36th, with France 29th, Russia 30th and the United Kingdom 34th.

Canada ranked 66th, a fall of six spots from the previous report.

The Institute counted 40 deaths in 12 attacks within the year in North America, but a list of each attack considered was not immediately available. The deadliest was in San Bernardino, Calif., when 14 were killed by radicalized married couple Syed Rizwan Farook and Tashfeen Malik.

The global economic impact of terrorism was assessed to be $89.6 billion with Iraq suffering the greatest impact, at 17 per cent of its Gross Domestic Product (GDP).

ISIS was the deadliest group in 2015, the report said, overtaking Boko Haram with attacks in 252 cities that led to 6,141 deaths.

However, Boko Haram's move into neighbouring countries Niger, Cameroon and Chad saw the number of fatalities in these countries increase by 157 per cent.