By Hamid Shalizi and Jessica Donati
KABUL, March 12 (Reuters) - A little-known militant group on Wednesday claimed responsibility for killing a Swedish journalist in the Afghan capital, saying he was a spy for British intelligence.
Nils Horner, 51, who worked for Swedish Radio and had dual British-Swedish nationality, was shot dead outside a restaurant one Kabul's most heavily guarded districts on Tuesday, underscoring growing insecurity threatening next month's elections.
"Nils Horner was killed in this attack. He was not a journalist. He was a spy for (MI6)," the group, Fedai Mahaz Tahrik Islami Afghanistan, said on its website.
Fedai Mahaz, or "Suicide Front", describes itself as a splinter group of the Afghan Taliban-led insurgency but the Taliban denied any connection.
"This group is not part of the Islamic Emirates. They only try to defame us," said a Taliban spokesman.
Kabul's police chief said he heard Fedai Mahaz had claimed responsibility, but did not have information about them because they were not active in the Afghan capital.
Horner was working for a Swedish broadcaster and had only been in Afghanistan for a couple of days.
Fedai Mahaz's website contains material outlining the group's opposition to the opening of an office for the Taliban in Qatar for peace talks in June last year.
More recently, the same group claimed responsibility for assassinating the provincial governor of Logar province in October. The attack was subsequently condemned by the Taliban because it was carried out in a mosque.
A Western embassy official said the group's suggestion that Horner was a secret agent was "fanciful" but the episode could point to a sinister new trend in which militants were now seeking to pick off random Westerners from the street.
"It kind of all points to being opportunistic, but we can't be sure," the diplomat said. "This whole claim on the website about him being in the Secret Intelligence Service (MI6) and not a journalist is just complete nonsense."
Tuesday's attack came as Afghanistan prepares for the withdrawal of NATO forces and landmark presidential elections scheduled for April 5. The Taliban have threatened to attack anyone who takes part. (Editing by Maria Golovnina and Nick Macfie)