New analysis of more than 4000 terrorist attacks within OECD countries over the past 15 years shows they are rapidly becoming more deadly.
The Institute for Economics and Peace (IEP) survey for Australia's terrorism insurance industry shows deaths caused by terrorism jumped by more than six times in the past two years.
The analysis found 592 attacks killed 77 people in 2014 in the 34 Organisation for Economic Cooperation and Development (OECD) countries, and a year later 731 attacks killed 577 people.
Half of the worst terrorist attacks since 2000 in OECD countries have occurred since 2015.
However, attacks on OECD countries still accounted for only 3 percent of total deaths from terrorism, registering 57 attacks that killed more than 10 people since 2000. In the rest of the world in that period, there were more than 3500 attacks on this scale.
Institute spokesperson Alex Gee said there was fear of a further spike, if Islamic State's (IS) military reversals in Syria and Iraq pushed thousands of foreign fighters back to western countries.
"The lone wolves' attacks are a lot less deadly than the directly coordinated attacks by [Islamic State] and that's another reason why ... governments with citizens who are possibly returning from Syria are particularly worried that they have had the training and they are the ones who can carry out much more deadly attacks," Mr Gee told RNZ.
The Nice truck attack in July - which killed 86 people - was an exception, a lone-wolf type attack with a high number of people killed.
In 2015, of the 34 countries in the OECD:
- 21 experienced a terrorist attack
- 11 recorded at least one death from terrorism
- Nine recorded the highest levels of terrorism since at least 2000
- Five had the most deaths since at least 2000
- There were more terrorist incidents in Australia in 2014-2015 than in the preceding 15 years combined
The IEP analysis showed unconventional attacks were on the rise and half of all plots with a link to Islamic State had been conducted by lone wolves.
"So France for instance, 90 percent of the terrorism there has happened in the last two years," said Mr Gee.
"Countries that have previously been fairly immune, like New Zealand, could see a future risk."
All types of attacks were becoming more deadly, with fatal attacks rising from one in six attacks to more than one in five.
IS was now responsible for half of all attacks and 36 percent of all terror-related deaths in the OECD. Kurdish separatist groups in Turkey were the next most deadly.
Turkey was the worst hit of any OECD country, followed by France and the United States. Belgium and Germany round out the top five for numbers of deaths in 2015 and 2016.
Almost a third of IS-linked attacks were in the US.