Arrested members of a local Islamic group sit outside a police station alongside their seized possessions in Kano, Nigeria, on Monday. (Associated Press)

Fighting between Islamist rebels and government forces in northern Nigeria continued for a third straight day, forcing hundreds of people to flee their homes and bringing the total number of civilians displaced to 4,000.

It is not known exactly how many have died amid the fighting in the north, particularly in the city of Maiduguri.

Reports on Tuesday indicated around 150 people had been killed in four northern states since Sunday.

That toll cannot be independently verified, and many observers fear that number has now mounted. Most of those killed are rebel forces, say police.

Relief official Apollus Jediel said about 1,000 people had abandoned their homes Wednesday, joining 3,000 displaced this week in four states caught up in the violence.

The government blames an extremist group known by several names, including Al-Sunna wal Jamma, or "Followers of Mohammed's Teachings" in Arabic, and Boko Haram, which means "Western education is sin" in the local Hausa dialect.

The group seeks to impose Taliban-style rule — based on strict interpretations of Islamic law — throughout the country.

Trouble began Sunday

Reporters on the ground say the trouble started with militants attacking a police station in Bauchi state Sunday. Then they attacked police in Kano, Yobe and Borno, of which Maiduguri is the capital.

Nigerian President Umaru Yar'Adua, however, said police attacked the militants first. He downplayed the violence, saying the situation is now "under control."

Some of the violence in several northern towns subsided Tuesday after authorities imposed curfews and dispatched security forces onto the streets to quell the attacks.

But people around Maiduguri railway station area, a stronghold of the sect, said Wednesday they were kept up all night by running gun battles.

From dawn, people started streaming out, carrying bundles of belongings and cooking pots and braziers.

Sporadic bursts of gunfire erupted there Wednesday morning.

Also Wednesday, police freed about 100 women and children held by militants in a building in Maiduguri.

The BBC reported that many of the women claimed they were the wives of rebel fighters and that they were forced to travel to the city from other parts of the country.

Nigeria's 140 million people are nearly evenly divided between Christians, who predominate in the south, and primarily northern-based Muslims.

Shariah law was implemented in 12 northern states after Nigeria returned to civilian rule in 1999 following years of oppressive military regimes. More than 10,000 Nigerians have died in sectarian violence since then.

With files from The Associated Press