The group's leader had not fallen into line with ISIS instructions, including by ignoring calls for Boko Haram to stop using children as suicide bombers.
Big construction company has seen shares plunge due to concerns about debt, stalled projects.
Another 60 people are left wounded after shooting, burning and explosions from three suicide bombers continued for nearly four hours on Saturday.
Islamic militant group Boko Haram may be responsible.
London-based human rights group says Nigerian army responsible for deaths of more than 8,000 people 'murdered, starved, suffocated, tortured to death.'
Millions across Africa's most populous country, however, make it to the ballot box in safety in the most closely contested presidential race in the nation's history.
The pledge of allegiance was attributed to Boko Haram leader Abubakar Shekau.
There were two explosions at two markets and a third blast at a bus station in Maiduguri, witnesses and the local government said.
'Weapons and equipment were also captured and some destroyed,' defense spokesman Major-General Chris Olukolade said in a statement.
In run-up to Nigeria's general elections, scheduled for February 14 and then postponed to March 28 due to security concerns, Boko Haram has stepped up brutal attacks.