Nearly 900 inmates escaped in a prison break in Abuja, Nigeria’s capital city, officials said.
They blamed the attack on Islamic extremist rebels.
At least 443 of the 879 escapees are still missing, Umar Abubakar, a spokesman for the Nigerian Correctional Service said.
Hundreds of others have either been recaptured or turned themselves in at police stations.
Officials will “track all fleeing inmates and return them to custody”, said Mr Abubakar.
The “very determined” rebels attacked the Kuje maximum prison in Abuja on Tuesday night with “very high-grade explosives”, killing one guard on duty, according to Shuaib Belgore, permanent secretary of Nigeria’s Ministry of Interior.
Explosions and gunfire were heard at about 10pm in the Kuje area when the attackers arrived and forced their way into the prison through a hole blasted in a wall.
The Islamic extremist rebels who attacked the prison have waged an insurgency in the country’s north-east for over a decade.
Their attack on the detention facility freed many of their members who are inmates, prison officials said.
“We understand they are Boko Haram. They came specifically for their co-conspirators,” said Mr Belgore.
The Kuje maximum security prison had nearly 1,000 inmates, including 64 suspects of the Boko Haram extremist group, all of whom have escaped, said Maj Gen Bashir Salihi Magashi, Nigeria’s minister of defence.
He told reporters security officials on the ground did “their best” to prevent the prison break.
“We are trying to see what we can do to ensure that all escapees are brought back,” he said.
As of Wednesday morning, bullet shells lay scattered around the prison premises, while helicopters hovered over the Kuje area as security agents combed nearby bushes in search of escapees.
A number of vehicles were razed during the late-night shootout.
Some recaptured inmates lay on the ground by the prison entrance near the bodies of those who died in the attack.
The Abuja jailbreak happened at around the same time that gunmen launched a daring attack on an advance security convoy preparing for the visit of Nigerian President Muhammadu Buhari in the north-west Katsina state.
Those attackers “opened fire on the convoy from ambush positions but were repelled by the military”, a presidential spokesman said.
Nigeria’s jihadi rebels and other armed groups have carried out several prison breaks in the country’s north-east in recent years, but this is the first in the capital city in recent years.
In 2021, more than 2,500 inmates were freed in three prison breaks.
At least 4,307 inmates have escaped from Nigeria’s prisons since 2017, Lagos-based online newspaper TheCable reported this month, based on compiled media reports.
Most of Nigeria’s recent prison breaks seem unconnected, although the attacks are carried out in a similar manner using explosives, according to security analysts.
A good number of those who have escaped in such attacks are awaiting trial.
Nigerian prisons hold 70,000 inmates but only about 20,000, or 27%, have been convicted, according to government data.
Nigeria’s extremist insurgency, carried out by Boko Haram and an offshoot known as the so-called Islamic State West Africa Province, is blamed for violence that has caused the deaths of more than 35,000 people and displaced more than two million people, according to the UN.
The prolonged instability, hunger and lack of health services caused by the insurgency have indirectly caused the deaths of more than 300,000 additional people, says the UN.
The extremists’ violence is the most serious security challenge in Nigeria, Africa’s most populous country with 206 million people, which also is battling violence in the north-west by rebellious herdsmen and a separatist movement in the country’s south.