(CNN) -- The Nigerian military said Thursday it killed one of the leaders of the Islamist extremist group, Boko Haram, which has waged an insurgency in the nation for years.

Mamadu Bama was the second-in-command, the military said in a statement.

He was killed this month along with his father, who was the group's spiritual mentor, the military said.

The militant group has not released any statement on the deaths.

Boko Haram has attacked various targets in the nation since 2009, murdering and kidnapping Westerners, and bombing schools and churches.

It is suspected to be behind a gruesome mosque killing this week. In that attack Sunday, militants brandishing automatic weapons killed 44 worshipers in the country's troubled Borno state. Around the time of the attack, the group released a video boasting that it was growing stronger.

Boko Haram translates loosely to "western education is forbidden/sinful." It holds all government authority in contempt and wants to establish a state in northern Nigeria under Islamic law.

Human rights groups have accused the Nigerian military of extrajudicial killings in its fight against the militant group.

"Soldiers have allegedly burned homes and executed Boko Haram suspects or residents with no apparent links to the group," Human Rights Watch said in a report this year. "Nigerian authorities have rarely brought anyone to justice for these crimes."