Islamic extremists said on Tuesday they killed more than 40 troops from a multi-national force in an attack on a convoy in north-east Nigeria — the fourth attack in three days following a lull as Nigeria's home-grown insurgency confronts a leadership struggle.

There were three earlier attacks on Sunday and Monday that led to the deaths of 18 people. Eight Christians were gunned down leaving a church service on Sunday, while there was also a further ambush on a convoy and a village leader and his son were beheaded. No one has claimed responsibility for these killings.