4 injured as blast hits Maiduguri in northeastern Nigeria, a day after suicide bomb killed 16

Rescue workers work at the scene of an explosion in Maiduguri, Nigeria, Saturday, May 30, 2015. A bomb exploded Saturday afternoon near Maiduguri's main market, after the city was attacked before dawn by Islamic extremists using rocket-propelled grenades, that killed at least 13 people, according to reports from local residents. (AP Photo/Jossy Ola) (The Associated Press)

A man inspects a house damaged in Saturday's rocket propelled grenades by Islamic extremist in Maiduguri, Nigeria, Sunday, May 31, 2015. A bomb injured four people in a market Sunday in Maiduguri, a day after the northeastern Nigerian city was hit by a suicide bomber who killed 16 in a mosque. (AP Photo/Jossy Ola) (The Associated Press)

A man inspects a house damaged in Saturday's rocket propelled grenades by Islamic extremist in Maiduguri, Nigeria, Sunday, May 31, 2015. A bomb injured four people in a market Sunday in Maiduguri, a day after the northeastern Nigerian city was hit by a suicide bomber who killed 16 in a mosque. (AP Photo/Jossy Ola) (The Associated Press)

A witness says a bomb injured four people in a market in Maiduguri in northeastern Nigeria, a day after a suicide bomber killed 16 in a mosque in the same city.

Jafar Aminu, a trader at Gamboru market, said the explosion on Sunday was near the Nigeria Customs House in Maiduguri. Nigeria's Islamic extremists, Boko Haram, are suspected for the explosions.

An official of a self-defence group in Maiduguri, Abbas Gava, said the explosive may have been concealed in some sacks of charcoal. He said one of the injured lost a hand. He said Gamboru market has suffered several such attacks in the last three years.