MAIDUGURI, Nigeria (AP) — Suspected members of a radical Muslim sect killed three people in a van blast near a military checkpoint, a Nigerian official said yesterday, the latest in an escalating series of attacks in the country’s restive northeast.

Major General Jack Nwachukwu Nwaogbo, the commander of the Joint Military Taskforce, said an explosive went off under the van Monday evening as its driver slowed down at a military and police checkpoint in the city of Maiduguri. The blast killed the driver and two passengers.

Authorities blamed a radical Muslim sect locally known as Boko Haram for the bombing, one of many attacks that have targeted security officers, local leaders and clerics in and around Maiduguri over the last year.

They say civilians are not cooperating and that some are helping Boko Haram carry out their attacks.

“Without the cooperation of residents, the Joint Military Taskforce cannot do anything,” said Nwaogbo, who leads a team of soldiers and police officers specially mobilised to fight Boko Haram in Borno state.

Unrest in the area has escalated ever since the group 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.

The University of Maiduguri announced Monday that it was shutting down indefinitely over threat letters attributed to the group.

“We can no longer guarantee the safety of our students,” said university spokesman Ahmed Mohammed. “If anything happens to our students, the university will be held responsible.”

Some 35,000 students are enrolled in the public university. Police in Maiduguri also banned motorcycles last week in an attempt to stop the group from committing motorcycle-mounted attacks. That move put 7,000 motorcycle taxi drivers out of work.

A military and police operation that left six civilians dead Saturday has stirred new fears among Maiduguri residents who worry they could get caught in the fight against the Islamic militants.

Hundreds gathered at bus stations yesterday morning to leave Maiduguri amid the unrest. Those who could not get buses boarded vans normally used to carry goods.

“Out of compassion, we are carrying people for (about $3), half the price that buses and taxis are charging,” said truck driver Yakubu Isa as he readied to depart for Kano, a northern city about some 350 miles away.

But recent attacks have shown that the group has broadened its reach across Nigeria’s Muslim-dominated north.

Boko Haram claimed responsibility in an unverified statement for a June 16 bombing that left two dead at national police headquarters in the capital of Abuja. Authorities suspect the group is responsible for a bomb attack Sunday that killed three people outside a church in a city just north of Abuja. Another blast in a district known for its busy nightlife about 120 miles from Abuja, wounded 20 people a few hours later.

Boko Haram, whose name means “Western education is sacrilege”, has asked for the strict implementation across Nigeria’s Muslim-dominated north and the prosecution of high-ranking officials whom it blames for the death of its leader Mohammed Yusuf. Yusuf died in 2009, while in police custody.