Deaths from terrorism declined globally but saw a six-fold increase in developed countries in 2015 compared to 2014, a report said released Wednesday.

Data gathered for the 2016 edition of the Global Terrorism Index (GTI) showed that such deaths in OECD countries, a group of mostly rich states, rose from 77 in 2014 to 577 in 2015.

This trend reflects how groups such as the so-called "Islamic State" (IS) suffered military defeats at home but orchestrated more foreign attacks. Some 313 terrorism deaths in developed countries were caused by IS-affiliated attacks.

France and Turkey were the worst affected countries in the Organization for Economic Cooperation and Development (OECD). Among the high-profile incidents were last November's Paris attacks where "IS" gunmen and suicide bombers targeted the Bataclan music venue, the Stade de France soccer stadium and several cafes, killing 137 people and injuring 368.

The worst terror incident in Turkey in 2015 was the October bombing in Ankara, where two explosives detonated outside the central train station. The attack killed 105 people and injured 400.

While Turkey and France suffered the most deadly attacks, they were far from the only countries to suffer terror-related deaths. Some 21 of the 34 OECD countries experienced at least one terror attack in 2015. Denmark, France, Germany, Sweden and Turkey all suffered their worst death tolls from terrorism since the index launched in 2000.

These countries have seen a sustained threat in 2016. Germany experienced IS"-linked attacks this summer, including an axe attack on a train in Würzburg and a suicide bombing in Ansbach.

German police have been swift in identifying and arresting "IS"-affiliated terror cells. On Tuesday, police raided more than 200 homes and offices of suspected "IS" sympathizers across 10 federal states.

Steve Killelea, Executive Chairman of Institute for Economics and Peace, an Australian think tank that publishes the annual index, said, "The attacks in the heartland of Western democracies underscore the need for fast-paced and tailored responses to the evolution of these organizations."

The index also illustrated how deaths from terrorism increased dramatically in recent years, particularly since the outbreak of the Syrian civil war.

Patterns recorded in the GTI show that terror attacks are more likely to occur in OECD countries with "poorer performance on socio-economic factors such as opportunities for youth, belief in the electoral system, levels of criminality and access to weapons."

Trends also show that foreign fighters who have fled to Syria to fight for "IS" generally have high levels of education but low incomes.

Ten percent fall in global terrorism deaths

The global number of terrorism-related deaths dropped 10 percent to 29,376 - the first overall decrease the GTI has recorded since 2010.

Iraq and Nigeria saw the biggest decreases, with a combined decline of 5,558 deaths. This was due namely to the Nigerian military's push against the terror organization Boko Haram and the reduced influence of "IS" in Iraq.

However, both countries remain among the world's most affected by terrorism, alongside Afghanistan, Pakistan and Syria. Together, the five countries accounted for 72 percent of all terrorism deaths in 2015.

"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," Killelea said.

"IS," which swept into a power vacuum in 2014, significantly stepped up its global presence in 2015, according to the GTI. It targeted 28 countries, compared to 13 the previous year. The group also orchestrated attacks in 252 cities and caused 6,141 deaths, surpassing Boko Haram as the world's deadliest group.

dm/sms (Reuters, Global Terrorism Index)