Twenty-two inmates have escaped from the main prison in Niger's capital during an attack by suspected Islamist militants, the government has said.
Justice Minister Marou Amadou confirmed that three guards had been killed in Saturday's prison break in Niamey.
He said weapons had been smuggled into the jail, and some of the escapees were prisoners facing terrorism charges.
It comes days after Islamists claimed twin suicide attacks on a military base and uranium mine, killing 25 people.
The Movement for Unity and Jihad in West Africa (Mujao) and an Al-Qaeda affiliate group, the Signed-in-Blood Battalion, said the attacks were retaliation for Niger's military intervention in Mali, which drove them out from the north earlier this year.
There are conflicting reports over events surrounding the prison incident.
Officials told the BBC on Saturday it started when a prisoner believed to be a Sudanese member of Mujao grabbed a gun from a guard, and shot dead three guards and a civilian.
Members of the group stationed outside the prison then opened fire, the officials said. Some were reported to have entered the building.
Residents also reported seeing gunmen firing at guards at the entrance to the prison at around 15:00 local time.
However, Justice Minister Amadou says it is likely the unrest started from within the prison itself after inmates managed to get hold of arms.
"It has emerged from initial investigations at the site that the aggressors obviously benefited from outside complicity regarding the weapon introduced into the prison," he said.
Nigerien gendarmes are reported to have later arrived at the prison to help the guards, who remained under fire for around 45 minutes. Police meanwhile blocked off roads leading to the facility.
The justice minister said that Malian national Cheibane Ould Hama, convicted of killing four Saudis and a US citizen, was among those who escaped and is being "actively sought".
Mujao is a splinter group of al-Qaeda in the Islamic Maghreb (AQIM), which formally announced its existence following the abduction of three aid workers in Algeria in October 2011.
It says its objective is to spread jihad to West Africa rather than confine itself to the Sahel and Maghreb regions - the main focus of AQIM.