Abuja, July 30 Nigerian police said Tuesday a manhunt has been launched for a group of gunmen who allegedly opened fire at a security checkpoint in the country's southeastern state of Imo, killing five, including four local police personnel, late Monday.

A trader near the security checkpoint was also killed during the incident in Irete, in the Owerri West Local Government Area, Henry Okoye, a spokesman for the police in Imo, told Xinhua over the phone Tuesday.

Police accused the outlawed Indigenous People of Biafra/Eastern Security Network, a militant group in southeastern Nigeria, of masterminding the attack.