Suspected jihadists using guns and explosives smashed their way into a prison near the Nigerian capital, freeing hundreds of inmates in an operation to release jailed comrades, the government said on Wednesday.
The brazen attack on the outskirts of Abuja came hours after an ambush on a presidential security convoy in the northwest, in a fresh illustration of Nigeria's security crisis.
Residents reported loud explosions and gunfire late Tuesday near the Kuje medium-security prison just outside the capital.
Security forces cordoned off streets in the area early Wednesday.
Outside the jail, the burned-out wreckage of a bus and cars marked the scene of the attack, and yellow police tape was stretched across a destroyed part of the prison perimeter.
"We understand they are Boko Haram, they came specifically for their co-conspirators," senior interior ministry official Shuaibu Belgore told reporters on a visit to the prison.
"Right now we have retrieved about 300 out of about 600 who got out of the jail cells."
One security official was killed when the gunmen breached the jail using high-grade explosives.
"We heard shooting on my street. We thought it was armed robbers," a local resident said. "The first explosion came after the shooting. Then a second one sounded and then a third."
Belgore said some jihadists were housed in the general prison population and hundreds of criminal inmates escaped when the gunmen broke in.
Some prisoners surrendered while others were recaptured with military roadblocks set up around the penitentiary.
Security forces sent back around 19 recaptured inmates in a black van on Wednesday morning, an AFP correspondent at the site said.
Former top police commander Abba Kyari, who was being held in Kuje awaiting trial in a high-profile drug smuggling case, was still in custody, corrections service spokesman Abubakar Umar said.
Nigeria's security forces are battling Boko Haram and Islamic State West Africa Province (ISWAP) jihadists in the country's northeast, where a 13-year conflict has killed 40,000 people and displaced 2.2 million more.
Nigerian officials sometimes use Boko Haram as a general phrase to refer to jihadists or other armed groups.
The over-stretched military is also battling heavily armed criminal gangs known locally as bandits who terrorise communities in the northwest and central states with raids and mass kidnappings for ransom.
In the country's southeast, troops are dealing with separatist militias who demand an independant territory for the local ethnic Igbo people.
The Kuje prison raid took place soon after gunmen also ambushed an advance presidential security detail preparing for President Muhammadu Buhari's visit to his home state of northwestern Katsina.
Buhari was not in the convoy, but two officials were slightly wounded in the attack. It was not clear who was responsible.
"The attackers opened fire on the convoy from ambush positions but were repelled," the presidency said in a statement.
Attacks on prisons in Nigeria have happened in the past, with gunmen seeking to free inmates.
More than 1,800 prisoners escaped last year after heavily armed men attacked a prison in southeast Nigeria using explosives.
The attackers blasted their way into the Owerri prison in Imo state, engaging guards in a gun battle before storming the prison. Imo state lies in a region that is a hotbed for separatist groups.