Suspected Boko Haram fighters attacked a military base in the northeast Nigerian city of Maiduguri and freed dozens of prisoners from custody, Nigerian military said.
An anonymous military source said on Friday that the rebels forced their way inside the barracks prison and "freed dozens of their members".
Asked about the report, defence spokesman Chris Olukolade told the AFP news agency that "many insurgents are in flight. Whether they were those who staged the attack or those who were held prisoner is not yet known."
In a separate statement, Olukolade said Boko Haram attacked the barracks "to boost their depleted stock of fighters" after being hit hard in recent weeks by military bombardments.
The army has used Giwa to detain hundreds of people suspected of belonging to the Boko Haram.The barracks is the headquarters of a 10-month-old government offensive against the group in northeast Nigeria.
President Goodluck Jonathan said on Friday he expects "maximum cooperation" from neighboring countries and warned their security could be affected by the uprising.
He was speaking with Cameroon's visiting interior minister, Rene Emmanuel Sadi, who assured that his government would never allow its territory to become a safe haven for the fighters. Nigeria last month closed hundreds of kilometres of border with Cameroon to prevent fighters using it as an escape route.
More than 2,000 people have been killed in violence over the last six months, security sources say.
Human Rights Watch on Friday said Boko Haram had carried out more than 40 attacks already in 2014, with more than 700 people killed, one of the highest rates of killing since the violence began.
President Jonathan intensified the military campaign almost a year ago to oust Boko Haram fighters from their stronghold in the poor and undeveloped northeast but it has failed to stem the bloodshed.
Source: Al Jazeera and agencies