Boko Haram militants are rampaging through northeast Nigerian villages and selectively killing men, boys and members of the same tribe as Chadian forces that have dealt major blows to the Nigerian Islamic extremists, witnesses said Thursday.

The fighters separated and killed people of the Shuwa-Arab community, which spreads across the border between Chad and Nigeria, while sparing people from the Kanuri tribe to which most Boko Haram militants belong, according to Mohammed Seit, a resident of Kala Balge village.

"They gathered the people in the market, and then separated the Kanuris from the Shuwa-Arabs; then they informed the Shuwa-Arabs that it was your tribesmen of Chad that are tormenting (Boko Haram)," he said. The militants said they were on a "revenge mission and to send message to your brothers the Chadians."

Scores have been killed and homes in dozens of villages burned down in the past five days, Seit told The Associated Press by telephone.

Nigeria's neighbor, Chad, has spearheaded a regional offensive and seized back major towns bordering Cameroon from Boko Haram in recent weeks.

In a separate attack Tuesday, at least 68 men and boys were killed in an attack on the rural community of Njaba, about 100 kilometers (80 miles) southeast of Maiduguri, the capital of Borno state, witnesses said.

"We, the women, were spared but every male including children of 12, 13 and 14 years old were killed", said Aminatu Mommodu.

She said she and other women were allowed to escape into the bush but crept back and counted the dead because she was looking for her husband and elderly parents too old to run.

Corpses, including many men with their throats slit, were in the mosque, since the attack came during dawn prayers. Others outside the mosque were shot, she said.

International concern has grown alongside casualties from the conflict. Some 10,000 people died in the Islamic uprising last year compared to about 2,000 in the previous four years, according to the U.S. Council on Foreign Relations. Some 1.6 million people have been forced from the homes, including tens of thousands across borders.