Sources say the insurgents carried out the attack along the Maiduguri-Monguno road where two other humanitarian workers were kidnapped.
Panic was also reported in Damaturu, the Yobe State capital, as soldiers repel a Boko Haram attack.
Residents report heavy artillery shelling, particularly from the northern part of the town around Gashua road.
The Nigerian Army is yet to react to the latest developments.
