Just days after weekend suicide bombings, at least four people were killed in an explosion on a minibus just outside the northeastern Nigerian northeast city Tuesday morning, reports Anadolu Agency.

The commercial minibus with nine people onboard suddenly exploded shortly after it hit the Gubio highway, north of Maiduguri, the Borno provincial capital, near a military checkpoint, state police spokesman Victor Izuku told journalists.

"There was an explosion today along Gubio road just before the military checkpoint.

"According to a preliminary report, a pick-up van with nine persons onboard emerged from a bush path to join the road to Gubio town when it exploded, killing four of those onboard," Isuku said.

He said the other passengers were wounded, some critically, and suggested the death toll could rise.

Maiduguri, Boko Haram's birthplace and former theatre of insurgency, has seen a recent upsurge in bomb attacks after a two-month respite.

Last Saturday, two bomb attacks at a gas station and refugee camp for displaced victims of insurgency killed at least seven people, with 24 wounded.

A suicide bomber was also killed by military troops while attempting to scale the perimeter fence of the refugee camp on Sunday. A bomb disposal squad later detonated explosive devices strapped onto the bomber’s body.

Local army commander Brig. Gen. Victor Ezugwu appealed for calm, assuring residents of their safety.