( CNN ) -- A radical Islamist group has claimed responsibility for the murder of Swedish journalist Nils Horner . The Fidai Mahaz group said on its website Tuesday that it had `` targeted '' the correspondent on the Wasir Akbar Khan 15 Road in Kabul . The brief statement , attributed to the group 's spokesperson Qari Hamza , asserted that the slain man was a spy and `` special worker '' of British intelligence agency MI6 . Neither the statement , nor any other part of the group 's website , offered any proof that the splinter group was behind the killing , and officials have cast doubts on the veracity of the claim . `` It is an ongoing investigation , '' Sediq Sediqqi , a spokesman for the Afghan interior ministry , told CNN . `` The Afghan police force are working very hard to find out who really was behind this . `` We can not verify any claim by anyone or any group at this stage . '' Previous statements posted on the site claim attacks on American and other NATO troops , and on Afghan security forces . The group also said it was responsibility -- under a previous name -- for the assassination of Canadian permanent resident Arsala Jamal , who was the governor of the Afghanistan 's Logar Province . The group 's leader , Mullah Najibullah , also known by his nom de guerre Umar Khatab , is at odds with the Taliban leadership and has openly called them `` traitors . '' His faction is opposed to the Taliban 's attempts at detente . Qari Yusuf Ahmadi , a Taliban spokesman , told CNN that he had no idea who the group was , and said that the Taliban had no relationship with it . A dual British and Swedish national , Horner worked as a reporter for Sweden 's Sveriges Radio , mostly covering Asia and the Middle East . The 51-year-old recently moved to Hong Kong and had visited Afghanistan several times previously . He was gunned down in broad daylight on a Kabul street Tuesday . A Lebanese restaurant near the site of the shooting was attacked in January . The brazen killing comes at a time when Afghanistan is preparing for next month 's presidential elections , and ahead of NATO 's planned withdrawal of troops by the end of 2014 . READ MORE : Swedish journalist shot dead in Kabul . Masoud Popalzai in Kabul contributed to this report .
Fidai Mahaz splinter group claims it was behind the murder of Swedish journalist Nils Horner . Many skeptical of the group 's assertion . Radical group is at odds with the Taliban -- and even more extremist . Killing comes at a delicate time for Kabul and Afghanistan .