The blast occurred at Kalam in the Lake Chad region, which has been battered by attacks from militants crossing from neighbouring Nigeria.
At least eight soldiers have been killed and many others wounded after their vehicle struck a landmine laid by suspected militants in western Chad.
The blast occurred on Wednesday at Kalam in the Lake Chad region, which has been battered by attacks from militants crossing in from neighbouring Nigeria.
Officials, speaking on condition of anonymity, put the toll at eight or nine dead and between 11 and 21 wounded.
A security source in Nigeria also gave the figure of nine dead and said the device had apparently been laid by the Daesh-affiliated ISWAP, a splinter group of Nigeria's Boko Haram.
One of the fatalities was a commander in the gendarmerie, the Chadian military source said, adding that exchanges of gunfire broke out later Wednesday between troops and militants in Bakaram, in the same region.
Boko Haram's insurgency, launched in northeast Nigeria since 2009, has killed 35,000 people and displaced around two million from their homes.
The violence has spread to neighbouring Niger, Chad and Cameroon, prompting the formation of a four-nation regional coalition of which the Chadian army is a key component.
In March, Chad's armed forces suffered their biggest single-day loss, when 98 soldiers were massacred in their base at Bohoma, on the banks of Lake Chad.
In response, President Idriss Deby launched an offensive from March 31 to April 3, declaring at its end that there was not a single militant left in the Lake Chad region.
N'Djamena claimed a thousand "terrorists" had been killed in the crackdown.