Multiple bomb blasts late on Friday in Nigeria's second largest city Kano were coordinated attacks on security targets that killed at least seven people, the police said on Saturday.

The attacks prompted the government to announce a dusk-to-dawn curfew in the city of more than 10 million people.

Kano, like other northern cities in Nigeria, has been plagued by an insurgency led by Islamist sect Boko Haram, blamed for scores of bombings and shootings, aimed mainly at government targets, that are growing in scale and sophistication.

At the moment, seven casualties have been confirmed from different locations of the attacks, police media officer Olusola Amore said in a statement.

The statement said the police are doing their best to bring the situation under control ... (we are) appealing to members of the public to come forward with information on the identity and location of these hoodlums.

The police said eight locations were attacked, including police headquarters, three police stations, the headquarters of the secret services and the immigration head office.

Witnesses said smoke billowed from the police headquarters after the blast blew out its windows, wrecked its roof and triggered a blaze that firefighters struggled to control.

A bomb attack on a Catholic church just outside the capital Abuja on Christmas Day, claimed by Boko Haram, killed 37 people and wounded 57.

The main suspect in that attack, Kabiru Sokoto, escaped from police custody within 24 hours of his arrest, and police have offered a 50 million naira ($309,600) reward for information leading to his recapture.

Police arrested him on Tuesday and he escaped when their vehicle came under fire while they were taking him from police headquarters to his house in Abaji, just outside Abuja, to conduct a search there.

Last August a suicide bomber blew up the U.N. Nigeria headquarters in Abuja, killing at least 24 people.

(Additional reporting by Felix Onuah, Segun Owen and Austin Ekeinde; Writing by Joe Brock; editing by Tim Pearce)