BAUCHI, Nigeria (AP) -- A car bomb exploded in a market in Nigeria's northeastern city of Maiduguri on Tuesday morning, and dozens of people are feared dead, witnesses said.

They immediately blamed Boko Haram, the Islamic extremist group whose birthplace is Maiduguri and which is accused of a series of recent bomb attacks in the West African nation.

Explosions last week targeted the biggest shopping mall in Abuja, Nigeria's central capital, killing 24 people; a medical college in northern Kano city, killing at least eight; and a hotel brothel in northeast Bauchi city that killed 10.

Boko Haram has attracted international attention and condemnation since its April abduction of more than 200 schoolgirls from a northeastern town who remain captive.

Tuesday's explosives were hidden under a load of charcoal in a pickup van, according to witnesses who spoke on condition of anonymity for fear of reprisals.

Trader Daba Musa Yobe, who works near the popular market, said the bomb went off just after the market opened at 8 a.m., before most traders or customers had arrived.

Other witnesses said they saw about 50 bodies, and that five cars and some tricycle taxis were set ablaze by the explosion.

They said the toll could have been worse but fewer than normal traders and customers were around because most people stay up late to eat during Ramadan, the Muslim month of fasting from sunrise to sunset.

A security official at the scene confirmed the blast, saying many casualties are feared. He spoke on condition of anonymity because he was not permitted to speak to the press.

Boko Haram has adopted a two-pronged strategy this year of bombings in urban areas and scorched-earth attacks in northeastern villages where people are gunned down and their homes burned.

On Sunday, suspected extremists sprayed gunfire on worshippers in four churches in a northeastern village and torched the buildings. At least 30 people were reported killed there.

The extremists have been attacking with more frequency and deadliness in recent months, defying security force and government assurances that they are getting the situation under control.