Fifteen people were killed on Thursday when a gang of armed men attacked two banks and a police station in the central Nigerian town of Offa, police told AFP Friday.
"They attacked the police station and at the same time attacked two banks," said Kwara state police spokesperson Ajayi Okasanmi, adding that nine police and six civilians died in the brazen assault.
The gang invaded a busy commercial area where several banks and the police station are located at around 15:50 (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 attack happened in part of Nigeria's volatile central region, which is notorious for criminal gangs and cattle rustling. Attacks on police are not uncommon.
Nigerian President Muhammadu Buhari has had to deploy security forces throughout Nigeria, West Africa's largest economy, to quell violence in the absence of a strong police force and rigorous legal system.
The gang attacks are a persistent problem for Nigeria, adding to security woes in a country already grappling with the Boko Haram Islamist insurgency.