(CNN) Boko Haram laughed off Nigeria's announcement of a ceasefire agreement, saying there is no such deal and schoolgirls abducted in April have been converted to Islam and married off.

Nigerian officials announced two weeks ago that they had struck a deal with the Islamist terror group.

The deal, the government said, included the release of more than 200 girls whose kidnapping at a boarding school in the nation's north stunned the world.

In a video released Saturday, the Islamist group's notorious leader fired off a series of denials.

"Don't you know the over 200 Chibok schoolgirls have converted to Islam?" Abubakar Shekau said. "They have now memorized two chapters of the Quran."

Shekau slammed reports of their planned release.

"We married them off. They are in their marital homes," he said, chuckling.

The group's leader also denied knowing the negotiator with whom the government claimed it worked out a deal, saying he does not represent Boko Haram.

"We will not spare him and will slaughter him if we get him," he said of the negotiator.

It wasn't clear when the video was made.

Mike Omeri, a government spokesman, said these assertions contradict those made in the group's talks with the Nigerian government.

Omeri said the government will do everything possible to verify the claims made in the video.

"We've heard about the video, and we can say the road to peace is bumpy -- and you cannot expect otherwise," Omeri said. "Nigeria has been fighting a war, and wars don't end overnight."

Nigeria said officials met with Boko Haram in Chad twice during talks mediated by Chadian President Idriss Deby.

The ceasefire deal announced on October 17 followed a month of negotiations with representatives of the group, said Hassan Tukur, an aide to Nigerian President Goodluck Jonathan.

After the deal was announced, the aide said final negotiations on the girls' release would be completed at a meeting a week later in Chad.

That day passed without any signs of the girls.

In the video, Shekau talked not of peace but of more violence -- promising more "war, striking and killing with gun."

This strategy appears to be playing out in parts of Nigeria, where Boko Haram fighters have continued deadly attacks on villages despite government claims of a ceasefire. More people have been abducted and scores killed in recent weeks, including one attack a day after the ceasefire that left eight dead.

JUST WATCHED Fleeing Boko Haram Replay More Videos ... MUST WATCH Fleeing Boko Haram 01:28

Days later, the Islamist terror group abducted at least 60 young women and girls from Christian villages in northeast Nigeria.

Heavily armed fighters left 1,500 naira, or about $9, and kola nuts as a bride price for each of the women abducted, residents said.

For its part, Nigeria isn't backing down.

It is stepping up its military campaign against militants and criminals in some parts of the West African nation, Nigeria's defense ministry said Saturday.

The military said its airstrikes and ground operations have repelled attacks against civilians in Adamawa and Borno, two states in the northeast that have been strongholds and frequent targets for Boko Haram.

Officials are "studying" the latest video, even as the military continues to recognize the talks aimed at assuring the release of the kidnapped schoolgirls, the ministry said.

Boko Haram, whose name translates to "Western education is sin" in the Hausa language, is trying to impose strict Sharia law across Nigeria, which is split between a majority Muslim north and a mostly Christian south. Like ISIS , it has ambitions for a caliphate, or religious state.

The group's attacks have intensified in recent years in an apparent show of defiance for the nation's military onslaught. Its ambitions appear to have expanded to the destruction of the government.

As part of its insurgency, it has bombed schools, churches and mosques, kidnapped women and children, and assassinated politicians and religious leaders alike.