Fifteen people were killed on Thursday when a gang of armed men attacked two banks and a police station in the Nigerian town of Offa, police told AFP Friday.
The brazen assault happened in part of Nigeria's volatile central region, where criminal gangs and cattle rustlers regularly attack security forces.
"They attacked the police station and at the same time attacked two banks," said Kwara state police spokesman Ajayi Okasanmi, adding that nine police and six civilians died in the violence.
The gang invaded a busy commercial area where several banks and the police station are located in broad daylight around 4:50 pm (1550 GMT), said Okasanmi.
"We are going all-out to ensure we arrest them," he said, adding that the haul from the robbery was not immediately known.
The robbers charged into the banks and shot people on the spot before making off with bags of cash on stolen motorbikes, said a witness.
"They split into two groups. One group attacked the divisional police station where they opened indiscriminate fire," said a resident who witnessed the attack, speaking on condition of anonymity.
"The other group attacked the two banks, shooting people they met inside, many of them in the head," he said.
"They carried away money in sacks from the banks and fled on motorcycles they seized from okada (motorcycle taxis) riders."
Senate President Bukola Saraki, one of Nigeria's highest-ranking politicians, commiserated with the victims of the "savage attack" in Offa.
In a statement released Friday, Saraki said the robbery "is a despicable act committed by cruel individuals."
Gang attacks are a persistent problem for Nigeria, adding to security woes in a country already grappling with the Boko Haram Islamist insurgency.
Nigerian President Muhammadu Buhari has had to deploy military throughout Nigeria, West Africa's largest economy, to quell violence in the absence of a strong police force and rigorous legal system.
On Wednesday, Buhari reiterated his support for $1 billion in emergency funding for weapons purchases to fight security threats across the nation, though critics warn that similar defense spending in the past has been tainted by corruption.
Police and military in the country were subject to intense scrutiny in February after it emerged that they were unable to repel Boko Haram fighters who stormed the town of Dapchi and abducted 111 schoolgirls.
Since then, 105 of the schoolgirls have been returned following negotiations with the Nigerian government, though six others -- including one Christian who refused to denounce her faith -- are still unaccounted for. The five others are believed to have died in the initial stages of the kidnapping.
Military and police are overstretched in Nigeria, which, along with fighting Boko Haram jihadists in the north, is battling militants and pirates in the oil-rich south, a simmering separatist movement in the east and a bloody battle between herdsmen and farmers spanning the vast central region.
Fighting fires on so many fronts takes an economic toll. This week Nigeria's central bank governor Godwin Emefiele said the "herdsmen-related violence" poses a key risk to the country's economic growth.