Nigerian authorities say gunmen attacked two police stations in separate parts of the country's north late Monday, killing seven people.

Authorities released details of the attacks Tuesday. In the deadliest incident, the assailants fired on a police station in the town of Tambuwal in northwestern Nigeria's Sokoto state, killing four officers and two civilians.

In the other attack, gunmen robbed a bank in the town of Gamawa in the northeastern state of Bauchi and detonated a bomb outside a police station while fleeing the area. One policeman was killed.

Nigerian authorities were investigating the attacks. Earlier in the day, police said they shot and killed a suspected suicide car bomber who tried to ram his vehicle into the police headquarters of the northeastern city of Maiduguri.

Officials blamed the foiled attack on Boko Haram, an Islamist group accused of carrying out a series of bombings and killings in Maiduguri, mostly targeting police and local officials.