Nine Chadian soldiers were also killed and 21 injured Tuesday in Gamboru as regional forces took the fight against the insurgents on to Nigerian soil for the first time, the Chadian army said.
"This toll is provisional," the Chadian military said in a statement, adding that troops were still combing the town on Nigeria's border with Cameroon for lingering rebel elements.
Around 2,000 Chadian troops backed by armoured vehicles poured across the border into Gamboru yesterday after the African Union last week backed a regional force to take on the extremists.
While the operation in Gamboru continued, the town of Fotokol on the other side of the border, in Cameroon, came under fresh attack from the jihadists.
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"The guys (Boko Haram) entered this morning. The fighting between them and our soldiers is very intense," a Cameroonian security source in Fotokol told AFP by telephone.
The Cameroonian troops had managed to repel the attack by mid-morning, after Chadian soldiers crossed back from Nigeria to help defend the town.
"We have routed this band of terrorists," the commander of the Chadian contingent Ahmat Dari told AFP Tuesday, vowing to "hunt them down everywhere."
Nigeria's military has drawn fierce criticism for failing to hold back the insurgents, who have stepped up their campaign of terror in country's northeast in the run-up to presidential and parliamentary elections on February 14.
In recent months the group has also carried out increasing cross-border raids, threatening regional security.
Chad's intervention reflects the growing nervousness among Nigeria's neighbours over the prospect of Boko Haram achieving its stated aim of carving out an Islamic caliphate on their borders.