In a separate development, police said the number of missing girls kidnapped from a school by the zealots has risen to 276 — an increase of more than 30 over the previous estimate.
Police Commissioner Tanko Lawan said the actual number of girls and young women abducted the night of April 14 was more than 300, with the number who have escaped also rising, to 53.
He told a news conference Thursday night in Maiduguri, the capital of Borno state in the northeast, that the figures keep increasing because students from other schools were brought into one school for final exams last month after all schools in Borno state were shut because of attacks by Islamic extremists.
Authorities had originally reported 129 girls kidnapped and the military had claimed to have freed all but eight of them — compounding confusion.
Unverified reports this week indicated some of the girls have been forced into "marriages" with their abductors and some have been taken across borders into Chad and Cameroon.
The attacks and the military's failure to rescue the teenagers have gravely undermined confidence in the government and the military, which had been claiming to have contained the 5-year-old Islamic uprising to a remote northeastern corner of the country.
Hundreds of kilometers (miles) away In Abuja, in central Nigeria, the government has said it is deploying 6,000 police to protect the May 7-9 World Economic Forum on Africa, with Chinese Premier Li Keqiang as an honored guest. The forum will be in Abuja, and Nigerian President Goodluck Jonathan last week assured delegates they would be safe. It attracts world leaders, policymakers, philanthropists and business leaders to discuss Africa's economic growth prospects.
The Thursday explosion occurred in a working-class suburb just a 15-minute drive from the presidential villa and the hotel venue of the conference.
Police Superintendent Frank Mba told reporters Friday the toll is up to 19 dead with as many wounded being treated in the hospitals. He said 66 people were wounded and taken to the hospitals, which have discharged six of them. He also said six cars were burned up in the blast.
He said police discovered three unexploded IEDs at the scene. Islamic militants in Nigeria often time secondary explosions to target rescuers and others drawn to a bombing.
Witnesses said a car laden with explosives drove close to the checkpoint and a man jumped out and ran as it blew up. A deafening explosion was followed by smaller ones as other cars caught fire and fuel tanks exploded, the witnesses said, speaking on condition of anonymity because of fears for their safety.
Obiora Enebike, who suffered injuries to his head and one hand, felt the shock wave after hearing a big bang. "I was trapped inside the car . I had to jump out of the car from one of the windows," he said of a lucky escape.
While there was no immediate claim for Thursday's bombing, it bears all the hallmarks of Boko Haram, whose name means "Western education is sinful." The group wants to create an Islamic state in Nigeria, which it claims would halt crippling corruption that keeps 70 percent of the people in Africa's richest nation impoverished.
Hours after the April 14 car bombing, which wounded at least 141 people, Boko Haram militants kidnapped the teenage girls at a school in the remote northeast, which is the insurgents' stronghold.
Every time the military trumpets a success against the militants, they seem to step up the tempo and deadliness of attacks. More than 1,500 people have died in the Islamic uprising this year, compared to 3,600 between 2010 and 2013.