( CNN ) -- On Saturday , in the wake of the rocket attack that downed Malaysia Airlines Flight 17 , Ukrainian President Petro Poroshenko urged the U.N. secretary-general to recognize the two main rebel groups in his country , the Donetsk People 's Republic and the Luhansk People 's Republic , as terrorist organizations . In a similar vein Monday , Poroshenko told CNN 's Christiane Amanpour that everyone must chose between the terrorists and the civilized world . Although any country can declare those two rebel groups terrorist in accordance with their national legislation , and so make it illegal for any of their nationals to provide them with support , the U.N. secretary-general can not , and nor can any other part of the United Nations , except possibly the Security Council . The reason is that there is no internationally agreed definition of terrorism . In fact , the debate on what terrorism means has been going on at the United Nations for at least 20 years , stuck in major disagreement over what may be considered legitimate when people are fighting for their right to self-determination . There are , however , many international conventions that define acts of terrorism , one of the earliest being the 1971 Convention for the Suppression of Unlawful Acts against the Safety of Civil Aviation , which would certainly cover the downing of the Malaysian airliner , so long as the act was shown to be intentional . But for Poroshenko , the rebels in the Donetsk and Luhansk regions were terrorists long before Flight 17 came down , and will remain so whether or not they are proved responsible . Russian President Vladimir Putin would see it differently . Although he backs President Bashar al-Assad 's characterization of all rebel groups in Syria as terrorists , in the Ukrainian case he believes that the rebels are exercising their rights to self-defense and self-determination . The two issues are not completely similar because the Syrian rebels are looking to change their government rather than their nationality , but in both cases use of the terrorist label has the same intention of inviting universal condemnation . It makes it harder to distinguish between what may be legitimate and what is not . And here lies one of the complexities of so many current areas of conflict around the world , where borders have become disputed not by the states that exist on either side , but by the people who live inside them and resent the identity or confinement that they confer . Since 9/11 , terrorism has come a long way from the isolated cases of assassination or attack that were common beforehand . A movement such as the Islamic State of Iraq and Syria , or ISIS , which even terrorist groups regard as terrorist , is as much an overt insurgency as a covert group of bombers and killers . In fact , the territory it currently controls makes it one of the wealthiest oil producers in the Middle East . Boko Haram , Al-Shabaab , al Qaeda in the Arabian Peninsula , all universally regarded as terrorist groups , control large areas of territory and aim to extend their reach . They are not like the Irish Republican Army , the Popular Front for the Liberation of Palestine , ETA or other historic organizations that more easily fit the popular concept of terrorism . Another issue that arises in the Ukrainian case is that if the rebels are terrorists , what does that make Russia ? State-sponsored terrorism has been less of an issue since the rise of al Qaeda , which seems to have done perfectly well without it . And while there are murky relationships between illegal armed groups and governments in parts of Africa and South Asia , state sponsorship on a scale that involves the supply of missiles capable of bringing down an aircraft at 30,000 feet would seem to deserve a name more closely related to conventional warfare . So we now have a nasty mix in many places around the world of terrorism , armed opposition groups and proxy wars , all dressed up in ambiguity , denial and obfuscation . And while these dirty wars drag on , only one thing remains constant -- the dead bodies strewn around the fields and towns , whether fallen from the sky or just lying where they stood . It does n't much matter whether the international community regards the Ukrainian rebel forces as terrorists or not , there are no possible reasons or exculpatory factors that can excuse what happened to Flight 17 , if -- as seems to be the case -- it was brought down by a missile fired from territory under their control . Join us on Facebook.com/CNNOpinion .
Ukraine President : pro - Russian rebels should be called terrorists . Richard Barrett : There 's no internationally agreed definition of terrorism . Under ' s definition , Malaysian plane 's downing would be illegal -- but only if intentional . Barrett : The world is seeing a merging of terrorist states and quasi - states .