The Islamic State West African Province (ISWAP) claim they killed the captives to avenge for the killing of their leaders Abu bakr al-Baghdadi and Abul-Hasan Al-Muhajir in Iraq and Syria.
A video released on Wednesday showed 13 hostages, 10 believed to be Christian and three Muslims. ISWAP claimed they spared the lives of two of the Muslims, local media reported.
The deaths came after an earlier video saw the hostages plead with the Christian Association of Nigeria (CAN) to negotiate their release.
In a statement, ISWAP said: ‘We killed them as a revenge for the killings of our leaders, including Abu bakr al-Baghdadi and Abul-Hasan Al-Muhajir in Iraq and Syria.’
United Nations Secretary-General Antonio Guterres offered his condolences, with his spoken Stephane Dujarric saying in a statement: ‘The Secretary-General is deeply concerned about reports that civilians have been executed, and others abducted, by an armed group in northern Borno State, northeastern Nigeria.
‘He expressed his deepest condolences to the families of the victims and reiterates the solidarity of the United Nations with the people and Government of Nigeria.’
Jihadis Boko Haram and its IS-affiliated Islamic State West Africa Province faction have recently stepped up attacks on military and civilian targets in Nigeria.