|The area in and around Maiduguri has seen an escalating series of attacks in recent months [EPA]
Suspected members of a hardline Muslim sect have killed three people in a van blast near a military checkpoint in northeast Nigeria, an official said.
An explosive went off under the van late on Monday as its driver slowed down at a military and police checkpoint in the city of Maiduguri, Major General Jack Nwachukwu Nwaogbo, the commander of the Joint Military Taskforce, said on Tuesday.
Authorities blamed the attack, which killed the driver and two passengers, on Boko Haram, which seeks a wider application of Islamic law across Africa's most populous nation.
The bombing comes as the latest in an escalating series of attacks in the restive region that have targeted security officers, local leaders and clerics over the last year.
Thousands have fled Maiduguri over the past two days fearing more attacks, residents said on Tuesday. Soldiers have also been accused of shooting civilians in the area.
One resident, Mainasara Mukhtar, told the AFP news agency he was leaving the area for fear of similar violence in his neighbourhood.
"Fliers were anonymously distributed in the neighbourhood warning of impending attacks and residents moved out to avoid being killed by soldiers as it happened in Kalari [neighbourhood]," he said.
"Most of us are leaving town because we have nowhere else to move in the city."
The University of Maiduguri on Monday announced that it was shutting down indefinitely over threat letters attributed to the Boko Haram group.
"We can no longer guarantee the safety of our students,'' Ahmed Mohammed, the university spokesman, said. "If anything happens to our students, the university will be held responsible.''
The bulk of the university's 35,000 students are drawn from other areas of the country.
Unrest in the area has escalated ever since Boko Haram vowed to step up attacks in an unverified June statement. Signed claims of responsibility and threat letters have emerged as a new trend in the operations of this once low-key group.
Hundreds of troops have been deployed to Maiduguri in a bid to stop the sect, and a shootout between soldiers and suspected sect members last weekend left at least 11 people dead.
Military officials said those killed were Boko Haram members, but residents allege that soldiers had shot civilians and burnt their houses, accusing them of complicity in the group's attacks.
Major General Nwaogbo defended his troops, saying they would not target innocent people.
"Soldiers are not animals who will be killing people indiscriminately. Anybody shot or killed by soldiers must have attacked them or is armed, which means he is part of the group we are out to tackle."
"My men are not responsible for the exodus because even before the deployment of soldiers people have been leaving the city," he said.
Boko Haram launched an uprising in 2009 that was put down by a brutal military assault which left hundreds dead and destroyed its mosque and headquarters in Maiduguri.
But the sect seemed to re-emerge last year with hit-and-run shootings targeting police, soldiers, politicians and community leaders.
It has also attacked police stations and churches, as well as raided a prison. Bomb blasts have become more frequent and far more deadly in recent months.
While Boko Haram has claimed to be fighting for the establishment of an Islamic state, the motives behind certain attacks remain unclear.