Kano - Boko Haram fighters have raided village on the border with Cameroon, apparently in reprisal for a Chadian offensive against its hideouts, residents told AFP on Friday.
Scores of heavily armed militants on Wednesday rampaged through more than a dozen villages in the Kala-Balge district in Borno state, shooting, hacking residents to death and razing homes.
Hundreds of residents fled across the border into Cameroon, prompting Chad - part of a regional coalition against the Islamists - to respond by bombarding rebel positions, they said.
"They targeted mainly Shuwa tribesmen, who are from the same ethnic group as a large number of the Chadian troops," said Adum Walfannea, himself a Shuwa Arab, from Anguduram village.
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Kurso Khala, who fled one of the worst-affected villages, Mudu, said the militants besieged a local market and blocked all but one entrance.
"They would ask if a person is Kanuri or Shuwa before asking him to go," said Khala by telephone from Fotokol, across the border from the Nigerian town of Gamboru in the far north of Cameroon.
"Once a person was identified as Shuwa he would be shot in the back as soon as he stepped out of the market entrance to leave."
Walfannea and Imar Koshnana, from Musiye village, both said the death toll from the attacks could be high but there was no official confirmation of numbers.
News of the raids come as Nigeria's military trumpets its success in recapturing several towns from Boko Haram and after President Goodluck Jonathan said the "tide had turned" against the militants.
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Details were slow to emerge because the insurgents have destroyed telecom masts since the insurgency began in 2009.
The attacks follow a Chadian ground and aerial offensive against Boko Haram enclaves in the Kala-Balge district that began on February 17 after troops seized the strategic town of Dikwa.
Residents said Boko Haram suffered heavy casualties in the Chadian attacks, which were near the group's Sambisa Forest stronghold, where they have long had camps.
One resident from the herding village of Gonori near Gamboru, Umar Sanda, said troops fought back after Boko Haram stole more than 400 cattle and killed four residents in a pre-dawn raid on Tuesday.
"For more than two hours we kept hearing sounds of gunfire and explosions," he added. "The Chadian troops killed scores of the Boko Haram gunmen and recovered our cattle."