Suspects arrested in deadly bank robbery, attack on police station in Nigeria Gunmen stormed banks and shot up a police station in central Nigeria.

Seven suspects have been arrested in the wake of a fierce attack on banks and a police station in central Nigeria this week that left more than a dozen people dead, police said.

A gang of gunmen raided the vaults of at least two commercial banks and opened fire at a police station in the city of Offa in Kwara State on Thursday, before fleeing the scene in their convoy with an undisclosed haul of cash. At least 17 people were killed in the attack, including eight police officers who were shot dead at the station, according to Kwara State Police spokesman Ajayi Okasanmi Jeffrey.

However, a source at Offa's general hospital told ABC News that 21 people, including nine police officers, who were brought to the facility following the attack had died. A doctor at a private hospital in the city confirmed three other victims had died there while he was on duty.

Speaking on condition of anonymity, an Offa resident who witnessed the attack told ABC News that the assailants separated into groups to simultaneously strike the banks and the police station.

Kwara State Gov. Abdulfatah Ahmed, who's a former banker, has offered 5 million Nigerian naira for information leading to the arrest of the culprits. Kwara State Police confirmed to ABC News on Saturday that seven people had been arrested so far for their suspected involvement in the attack.

Abubakar Bukola Saraki, the president of Nigeria's Senate, visited Offa this weekend to meet with local authorities and victims' families. Saraki described Thursday's bloodshed as a "savage attack on unsuspecting citizens and establishments," and he vowed that "no stone will be left unturned" until the perpetrators are caught.

"It is my hope that Thursday’s incident that has left our people in Offa and Kwara State rattled and in grief will never reoccur," the Senate leader said in a statement Saturday.

Attacks on police and armed robberies are not uncommon in central Nigeria. The West African nation is also grappling with the Boko Haram terrorist group's nine-year insurgency hundreds of miles away in the northeast region.