Bodies (in the background) of suspected Islamists and their belongings lay in the streets of Maiduguri on Wednesday
Nigerian police have freed about 100 women and children being held by a radical Islamist sect in a building in the northern city of Maiduguri.
They told the BBC they had been held six days, living on dates and water.
Heavy fighting continues in Maiduguri where troops are besieging militants of the Boko Haram sect in an enclave.
Boko Haram is blamed for attacks on police stations and government sites in the north this week that led to the deaths of at least 150 people.
Boko Haram says it is fighting against Western education. It believes Nigeria's government is being corrupted by Western ideas and wants to see Islamic law imposed across Nigeria.
President Umaru Yar'Adua earlier ordered Nigeria's national security agencies to take all necessary action to contain and repel attacks by the extremists.
Boko Haram is led by Mohammed Yusuf, who has his base in Maiduguri, capital of Borno province.
About 1,000 people are inside the Maiduguri enclave, according to the military.
Security forces flooded into Maiduguri and began attacking Mohammed Yusuf's compound on Tuesday, shelling it with heavy weapons and exchanging gunfire with militants.
Fierce fighting continued through the night and into Wednesday.
The militants are well-armed and have been keeping up a steady stream of fire, the officer commanding the operation, Col Ben Ahanotu, told the BBC.
He said there were at least 250 armed men guarding Mohammed Yusuf's home, which is also the headquarters of the sect.
Col Ahanotu also said papers and personal items found on the bodies of young men indicated that many had come from neighbouring Chad and Niger.
One Maiduguri resident, Adamu Yari, told Reuters news agency that soldiers and police were combing the whole city, searching house to house for Boko Haram followers.
Police in Maiduguri said they had discovered a building full of women and children who were being imprisoned on the edge of the city.
Pictures from Monday in Bauchi show the aftermath of violence
Those freed on Wednesday morning were mostly young women - mothers with small children, some of them nursing newborn babies.
An earlier report suggested the number of those freed was about 180 but the figure was later revised downward.
Many of the women told the BBC their husbands were followers of Boko Haram, and that they had been forced to travel to Maiduguri.
It is understood all of the women are from Bauchi State, the BBC's Caroline Duffield reports from Lagos.
In other states in northern Nigeria, reports are emerging of abductions linked to Boko Haram.
In Katsina State, 10 members of two families went missing last week.
Husbands told the BBC their wives and children had been offered the chance to learn the Koran by a cleric, after which they had been abducted.
They believe their loved ones are now in Maiduguri with, the men fear, Boko Haram.
Four states in northern Nigeria have been affected by Boko Haram unrest - Borno, Bauchi, Kano and Yobe.
A total of 103 deaths were officially reported in Maiduguri and reports say more than 50 people died in Bauchi and Yobe, but the true number of casualties may be much greater.
Sharia law is in place across northern Nigeria, but there is no history of al-Qaeda-linked violence in the country.
The country's 150 million people are split almost equally between Muslims in the north and Christians in the south.
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