Kano - Gunfire and explosions erupted in Maiduguri on Tuesday as soldiers moved into an area where members of Islamist group Boko Haram were believed to be hiding, residents said.
"There have been at least eight explosions in these neighbourhoods and soldiers have moved in with tanks and have taken over the whole area," one resident said.
Another said the area was largely deserted of residents after earlier signs that soldiers were preparing a crackdown. Alleyways had been sealed off ahead of Tuesday evening's violence, they said.
The explosions and gunfire began rocking the city at about 16:30 and could still be heard more than three hours later.
Residents said the area affected had been cordoned off and included the neighbourhoods known as Shehuri, Abbaganaram, Budum and Hausari. Military officials were not responding to phone calls.
"Since yesterday, residents of these areas have been deserting their homes," one of the residents said. "Explosions erupted in these neighbourhoods and soldiers cordoned off these areas."
The north-eastern city of Maiduguri is at the centre of Boko Haram's insurgency, which has claimed more than 1 000 lives since mid-2009. The group's mosque and headquarters were located there until they were destroyed in a 2009 military assault.
Nigerian troops have also been accused of abuses in Maiduguri, including burning homes and killing civilians in the wake of bomb attacks.
Thousands of residents have fled the city amid the spiralling violence.
On Monday, Boko Haram claimed responsibility for a weekend suicide attack on a church in the country's northeast which killed 15 people and wounded 40 others.
In the emailed statement to journalists, Boko Haram also threatened renewed attacks on journalists and media houses.
In Sunday's attack, a suicide bomber tried to drive an explosives-packed car into a church.
The attacker approached a checkpoint near the church in Bauchi State, which has previously been hit by Boko Haram and where tension between Muslim and Christian ethnic groups has led to violence in the past.
He was stopped at the checkpoint and instead rammed his car into the security gate around the church and set off his explosive device.
Boko Haram's attacks have grown increasingly sophisticated and have affected a wider geographical area, spreading from their base in the extreme northeast across the wider north and down to the capital Abuja, in the centre of the country.
It claimed responsibility for a suicide bombing of UN headquarters in Abuja in August which killed at least 25 people.
Its deadliest attack yet occurred in January in the northern city of Kano, when coordinated bombings and shootings left at least 185 people dead.