Story highlights The military kills more than 70 Boko Haram members in an operation in Borno state

They also fend off an attack on a military checkpoint in Yobe state's capital

21 suspected Boko Haram members die in fighting there

Boko Haram seeks to impose a strict version of Sharia law across northeastern Nigeria

More than 70 members of the Islamist extremist group Boko Haram have been killed during a Nigerian military operation in the northeastern state of Borno, an Army spokesman told CNN on Friday.

The military "remains on the offensive," according to Brig. Gen. Ibrahim Attahiru, who said the operation started Thursday and continued into the next day.

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This wasn't the only clash between Boko Haram and Nigerian troops of late.

Suspected members of the extremist group around 5:30 p.m. Wednesday (12:30 p.m. ET) attacked a military checkpoint in Damaturu, Nigeria's Joint Task Force reported in a statement. Also in northern Nigeria, Damaturu is the capital of Yobe state.

Special operations troops responded, waging "a fierce encounter with the terrorists in various parts of Damaturu ... for several hours," according to the Joint Task Force.

By the time that fighting was over, 21 suspected Boko Haram fighters were dead, the government group reported. Three vehicles were recovered, as were assault rifles, a rocket-propelled grenade, improvised explosive devices and 709 rounds of ammunition.

The military did not provide any information on its casualties.

"Law abiding citizens are enjoined to remain calm as the 3 Division Special Operation Battalion is on top of the situation," the Joint Task Force said, noting a 24-hour curfew was imposed throughout the state. "Any credible information should be passed promptly to security agencies for necessary action."

Last May, President Goodluck Jonathan put three states in the region under a state of emergency, giving Nigerian forces wide latitude in fighting the group, which human rights organizations say has killed more than 3,000 people since 2009.

Boko Haram, which means "Western education is sacrilege" in the Hausa-Fulani language, seeks to impose a strict version of Sharia law across northeastern Nigeria, if not the entire country.

The group has attacked various targets in the West African nation since its formation in the late 1990s, according to the U.S. National Counterterrorism Center , including killing and kidnapping Westerners, and bombing schools and churches.

Hundreds of its members, including its leader Mohammed Yusuf, died in July 2009 clashes with government forces. But the group did not stay down for long, and has remained an active and violent force in Nigeria.

In August, its militants allegedly went into a mosque in Borno state and killed 44 worshipers. The group released a video boasting that it was growing stronger.