The world’s most developed countries have suffered a dramatic increase in deaths as a result of terrorism in the last year, according to the new Global Terrorism Index, despite a drop in the global number of terrorism-related deaths.

The index shows Isis is now officially the deadliest terrorist group in the world, overtaking Boko Haram, after claiming responsibility for 6,141 deaths through attacks in more than 250 different cities in 2015.

And the number of countries in which Isis has carried out attacks more than doubled, from 13 in 2014 to 28 in 2015.

Globally, the number of terrorism-related deaths dropped 10 per cent in 2015 from the year before, which had been a record in the 16 years covered by the index from the Institute of Economics and Peace.

The fall in deaths has been driven by military action against Isis and Boko Haram in Iraq and Nigeria respectively, but the index suggests those groups have expanded their influence in neighbouring countries and regions.

A 650 per cent increase in deaths from terrorism in OECD countries and a marked rise in transnational terrorist attacks means the world is now a yet-more dangerous place in terms of terrorism, according to the IEP.

The 10 developed countries suffering the most deaths from terrorism Show all 10 1 /10 The 10 developed countries suffering the most deaths from terrorism The 10 developed countries suffering the most deaths from terrorism 10: Greece Greek Presidential Guards, or Evzones, take their place for a review by US President Barack Obama and his Greek counterpart Prokopis Pavlopoulos in Athens, Tuesday, Nov. 15, 2016. President Barack Obama arrived in Greece Monday morning on the first stop of his final foreign tour as president, the first visit to Greece by a sitting U.S. president since Bill Clinton in 1999 trip. (AP Photo/Lefteris Pitarakis) AP The 10 developed countries suffering the most deaths from terrorism 9: Denmark Shutterstock The 10 developed countries suffering the most deaths from terrorism 8: Austalia The incident allegedly took place in a primary school in Sydney Getty Images The 10 developed countries suffering the most deaths from terrorism 7: Sweden Ola Ericson/imagebank.sweden.se The 10 developed countries suffering the most deaths from terrorism 6: Mexico People talk to relatives at a section of the wall separating Mexico and the United States, as photographed from Playas Tijuana, in Tijuana, Mexico, November 6, 2016. REUTERS/Stringer FOR EDITORIAL USE ONLY. NO RESALES. NO ARCHIVES. Reuters The 10 developed countries suffering the most deaths from terrorism 5: Germany Afghan asylum seeker Shakira Sarwari, 27, and her two children, Mohammed, 17 months, and Setayesh, 7, are taken off a Munich-bound train in Salzburg, Austria, by German police Anthony Faiola/The Washington Post The 10 developed countries suffering the most deaths from terrorism 4: Israel Israeli Prime Minister Benjamin Netanyahu, attends the weekly cabinet meeting in Jerusalem, Sunday, Nov. 13, 2016. (Ronen Zvulun, Pool via AP) AP The 10 developed countries suffering the most deaths from terrorism 3: US US police have shot 698 people in 2016 so far. Four times more black than white people have been shot Getty The 10 developed countries suffering the most deaths from terrorism 2: France French policemen and security officers stand guard at the entrance of the Bataclan concert hall in Paris on November 12, 2016, a few hours before the reopening concert by British musician Sting to mark the first anniversary of the November 13 Paris attacks. Rock star Sting reopens the Bataclan on November 12, the revered Paris concert hall where jihadists massacred 90 people, with a hugely symbolic show to mark the first anniversary of France's bloodiest terror attacks. Scores of survivors of the Bataclan assault -- the worst of the gun and suicide attacks across the city that night which left 130 dead -- will attend the concert, the dominant event in a weekend of otherwise low-key commemorations. / AFP PHOTO / PHILIPPE LOPEZPHILIPPE LOPEZ/AFP/Getty Images Getty The 10 developed countries suffering the most deaths from terrorism 1: Turkey AP

Though the index identifies 274 distinct terrorist groups around the world, between them Isis, Boko Haram, al-Qaeda and the Taliban were responsible for 75 per cent of all terror-related deaths.

In terms of developed countries, 2015 was the second-deadliest year since records began. It was surpassed only by 2001, when the 9/11 attacks accounted for 2,996 deaths.

The index suggested there were lessons to be learned, such as the fact that only 0.5 per cent of terrorist attacks occurred in countries which have no involvement in foreign conflicts and low levels of “state-sponsored terror” - extra-judicial deaths, torture and imprisonment without trial.

The report found terrorism is also more likely to occur in OECD member 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.

Despite receiving far greater international news coverage than any other terrorist incident of 2015, the Paris attacks with a combined death toll of 136 do not even feature in the top 10 most deadly events of the year.

The most fatal attack of 2015 was in April in Qaim, Iraq, when Isis fighters rounded up and executed 300 civilians.

Other incidents in the top 10 include the bombing of the Russian Metrojet passenger plane in October 2015, which killed all 224 people on board, and the April attack on Garissa University in Kenya when al-Shabaab militants executed at least 154 people, mainly non-Muslim students.

Steve Killelea, Executive Chairman of IEP, said, “This year’s GTI report highlights the most complex set of dynamics in global terrorism in the last 16 years.

“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.