LONDON  - A United Nations investigation into the impact of drone strikes and targeted killings on civilians was launched in London on Thursday.Ben Emmerson, the UN special rapporteur on counter-terrorism and human rights, said there was a need for accountability when strikes went wrong.Emmerson, a British lawyer who is heading up the inquiry, said the huge expansion in the technology used in drones required a new legal framework to be put in place. “The exponential rise in the use of drone technology in a variety of military and non-military contexts represents a real challenge to the framework of an established international law,” he told a press conference in London.“It is both right as a matter of principle, and inevitable as a matter of political reality, that the international community should now be focusing attention on the standards applicable to this technological development.”The probe will focus on 25 case studies of attacks in Pakistan, Yemen, Somalia, Afghanistan and the Palestinian Territories and will report to the UN General Assembly before the end of the year. According to BBC, Emmerson told journalists in London that if unregulated the use of drones would continue to grow.The inquiry will assess the extent of civilian casualties, the identity of militants targeted and the legality of strikes where there is no UN recognition of a conflict.Defenders of drones say they minimise civilian casualties, but opponents say drone strikes can constitute extra-judicial killing and point to data suggesting hundreds of civilians have died in such strikes. Drones - or unmanned aerial vehicles (UAVs) - have become an increasingly potent weapon for nations seeking to target militants but there is increasing controversy over their toll on civilians. Drone attacks have been a key source of tensions between the US and Pakistan Between 2004 and 2013, CIA drone attacks in Pakistan killed up to 3,461 people - up to 891 of them civilians, according to research by the Bureau of Investigative Journalism. The vast majority of the strikes were carried out under the administration of President Barack Obama, it said.Some kinds of drone attacks - in particular ‘double tap’ strikes where rescuers attending a first blast become victims of a second - could constitute a war crime, Emmerson has previously said, according to the Guardian newspaper. Addressing journalists on Thursday, he denied the inquiry was unfairly singling out the US and Israel, saying 51 states had the technology to use drones.He said it was not a substitute for “effective, official and independent investigation” by states, and called for independent investigations where there was “plausible evidence of a war crime”. The inquiry will report to the UN General Assembly in the latter half of the year.