ABUJA, Nigeria — More than 100 people have been killed in a series of attacks in northern Nigeria’s largest city, officials said Saturday, in what appears to be the deadliest strike yet by a radical Islamist group.

The attackers in Kano on Friday evening struck eight government security buildings, the national police said, including the regional police headquarters, two local police stations, the local headquarters of the State Security Service, the home of a police official and the state police command headquarters.

The radical sect Boko Haram, which has carried out an escalating campaign of violence in its battle to impose its version of Islamic law across Nigeria, claimed responsibility. A letter distributed to reporters on Saturday said the attacks in Kano, Nigeria’s second-largest city, were retribution for the arrests and killings of members of the sect.

Residents in Kano described bloody scenes of chaos and confusion as bombs exploded and gunmen started shooting in the street.