Witnesses to the attack said that sporadic shooting was heard into the afternoon, while reports also emerged that a bomb exploded just hours after the prison raid.
Monday's attack came as Niger's parliament was set to vote on a proposal to send troops into neighboring Nigeria to help combat the insurgents on their home turf.
The terror group, which is currently in control of large swathes of northern Nigeria, has threatened to expand the reach of its self-declared caliphate into neighboring Niger, Chad, and Cameroon, and has multiplied its cross-border incursions in the past week.
On Wednesday, the Islamic extremists killed at least 70 people in a cross-border raid on the northern Cameroonian town of Fotokol. The insurgents were eventually pushed back by Chadian troops, with help from Cameroon's Rapid Response Battalion (BIR).
On Friday, Boko Haram fighters attacked the Doutchi bridge into Diffa, which straddles the Yobé River, the natural border between Niger and Nigeria. According to Niger's defense minister Mahamadou Karidjo, 109 insurgents were killed during Friday's attacks on Diffa and the nearby town of Bosso. Karidjo also said four troops and one civilian had died in the clashes.
The minister did not disclose the nationalities of the killed soldiers — Chadian troops are also deployed along the border to help stave off the Islamic extremist threat.
On Sunday morning, Niger's army repelled yet another attack on Diffa, after militants stormed the town on Saturday night. Residents of Diffa awoke to shelling and, later in the morning, militants set off a bomb in the town's pepper market, killing one and injuring at least 10, according to local officials. Minutes later, Defense Minister Karidjo escaped Boko Haram gunfire as he traveled to Diffa to honor victims of the militant group.
In response to Boko Haram's intensified attacks in the region, officials from Benin, Cameroon, Niger, Nigeria, and Chad met in Cameroon's capital Yaoundé on Saturday to formalize the creation of the FMM (Force Multinationale Mixte) multinational force, a regional military alliance to combat the militant group. An 8,700-strong force — to include troops, police officers and civilians — will be mobilized, pending a vote by the African Union security council and the UN.
French troops are already stationed in Diffa and in Bosso, as part of an initiative to support Chad and Niger's armies.
In a video released on Monday, Boko Haram leader Abubakar Shekau laughed off efforts by the regional coalition of Nigeria, Chad, Cameroon, and Niger, saying they would "lead to nothing."
Today, VICE News spoke to a 40-year-old NGO worker living and working in Diffa about Monday's attack. Speaking on condition of anonymity, he described the aftermath of the attack and shared his thoughts about the efforts to defeat Boko Haram.
VICE News: Can you describe the situation on Monday afternoon?
NGO worker: Things were calmer by midday, people had returned to the streets. We just heard a massive explosion over by the station and we can see smoke. The situation has been dire since Friday. People are worried and a small number of them — mostly young people — are fleeing to the west. Personally, I think I'll stay here and I'll encourage people to do the same. If we leave, we're playing into the hands of Boko Haram.
Are there any Boko Haram sympathizers in this part of Niger?
Yes, there are many Boko Haram supporters in Niger. In reality, whatever goes on in Nigeria easily crosses over into Niger. Both people have a lot in common — a common ethnic background, the same religion, the same socio-economic background and a shared culture. This makes the border incredibly porous. Boko Haram militants have a unique modus operandi: they infiltrate the local population in order to come out as a group and launch a collective assault. Which is more or less what they did last night when they stormed the prison. They were unable to reach the town via the bridge, which is well guarded, so they smuggled themselves in.
What are your thoughts on the national and regional campaigns to fight Boko Haram?
Unfortunately, Niger's army is not very powerful, and cannot destabilize Boko Haram alone. The population is more interested in the army defending our borders than in going off to fight Boko Haram on its own territory. What we really need is the support of the international community, as well as logistical help and support in the intelligence department. Whatever people say, we need the west for intelligence. I don't believe the African coalition [of the FMM] is enough.
Follow Pierre Longeray on Twitter: @PLongeray