Nigeria's military on August 14, 2013 said it had killed the second-in-command of Islamist group Boko Haram while repelling an insurgent attack earlier this month. (HO/AFP/Getty Images)

Nigerian soldiers have killed the second-in-command of the Islamist sect Boko Haram, an insurgency that has caused the deaths of thousands in the last three years, the Ministry of Defense said Wednesday.

It said Momodu Bama, who had a $155,000 bounty on his head, was killed along with 17 other members of the sect during clashes with the military on Aug. 4 in Bama, a town in the northeastern state of Borno.

“Momodu Bama has been personally leading the attacks against troops and innocent citizens in the communities of Yobe and Adamawa,” the ministry said in a statement.

“A specialist in manning the antiaircraft guns of the group, he is known to be vicious and heartless with a penchant for personally slaughtering and executing his victims.”

The ministry said Bama was identified by arrested militants.

Boko Haram’s leader, Abubakar Shekau, who is the only visible member of the group through appearing on Internet videos, says the army lies about victories over his fighters.

The military has announced the killing of senior members of the sect before, notably a spokesman called Abu Qaqa, only for a person using the same name to say he had not been killed.

Boko Haram — which wants to impose sharia, or Islamic law, in Nigeria’s north — and spinoff Islamist groups have become the biggest threat to stability in Nigeria.

The group’s name roughly translates as “Western education is forbidden.”

The military in Adamawa state, to the south of Borno, said Wednesday that it had killed two other top Boko Haram commanders in a gunbattle last week.

The two men were arrested near the town of Mubi last week and confessed that they planned an operation in Taraba state to the south, Mubi army chief Beyidi Marcus Martins told reporters.

The men died in a shooting that erupted after they took army officers to show them their hideout in Mubi. Several other sect members were also killed, Martins said.

Human rights groups have accused Nigerian soldiers of carrying out extrajudicial killings during their fight against Boko Haram. The army has always denied the accusations.

In mid-May, President Goodluck Jonathan declared a state of emergency and launched an offensive against the group in its stronghold in Borno, Yobe and Adamawa states in the northeast.

Gunmen suspected of belonging to Boko Haram killed at least 44 people and wounded 36 in an attack Sunday during prayers at a mosque in Borno state.

Boko Haram’s main targets are security forces or government officials, but it has carried out several attacks on Christian and Muslim worshipers, as well as schools and markets.