Gunfire and explosions rang out through Nigeria's main northern city of Kano on Tuesday as Nigerian forces battled Islamist militants in a raid on one of their hideouts, witnesses and the military said.
Residents of the Sabuwar Gandu area of Kano awoke to several loud blasts and a raging gun battle. There were no immediate reports of casualty figures.
"Our men just raided one of the hideouts of the elements ... where we discovered explosives and weapons," said a spokesman for the Joint Task Force (JTF) in Kano, Lieutenant Iweha Ikedichi.
After a relative lull, Boko Haram attacks have surged in the past few days, dampening hopes that tighter security in the north had drastically reduced their capability.
The shadowy sect says it is fighting to reinstate an ancient Islamic caliphate in Africa's most populous nation, whose 160 million people are split roughly evenly between Muslims and Christians along north-south lines.
"We were kept awake by bomb blasts and gunfire. It is really terrifying. We can't say where exactly the blasts are coming from. Everyone is indoors," Anthonia Okafor, a student at Kano university who lives in the Sabuwar Gandu area, told Reuters by telephone.
Hundreds have died in bomb and gun attacks across the north and in the capital Abuja since the Islamists launched their uprising in 2009, targeting authorities, security forces and more recently the north's Christian minority.
A bomb blast struck a police chief's convoy in eastern Nigeria's Taraba state on Monday, killing 11 people.
Gunmen attacked a university theatre being used for Christian services in the northern city of Kano and a church in northeast Maiduguri, Boko Haram's hometown, on Sunday. In total 19 people died in the attacks.
The insurgency has replaced militancy in the oil producing Niger Delta to become the main security threat to President Goodluck Jonathan's administration, and it has gained momentum since his presidential election victory a year ago.
Suicide car bombers targeted the offices of newspaper This Day in Abuja and in Kaduna last week, killing at least four people and demonstrating the sect's continued ability to carry out coordinated strikes.