Eleven soldiers have died and 50 civilians are missing in Burkina Faso following a suspected jihadist attack, the government says.
A supply convoy escorted by the army travelling to the northern town of Djibo, was targeted in an ambush on Monday.
The government called it a "barbaric attack", the AFP news agency says.
The region is facing a jihadist crisis which has killed thousands and displaced more than two million.
The military, led by Lt Col Paul-Henri Sandaogo Damiba, took power in a January coup, promising an end to the Islamist insurgency that started in 2015, but violence still rages.
Lt Col Damiba had been at the forefront of the country's fight against Islamist militants and even wrote a book on the subject last year called West African Armies and Terrorism: Uncertain Responses?
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It is not the first time a supply convoy has been targeted this month. On 5 September, at least 35 civilians were killed and 37 wounded after another convoy hit an improvised explosive device on a main road also leading to the north of the country.
The authorities say Monday's attack, which no-one has yet claimed responsibility for, caused significant material damage, leaving 28 wounded, including 20 soldiers, 1 Volunteer for the Defense of the Homeland (VDP) and 7 civilians.
It took place in the Gaskinde area of Soum province, where jihadist groups with links to al-Qaeda and Islamic State have ramped up attacks, according to the Reuters news agency.
Jihadists have also seized land and blockaded areas nearby to and surrounding the area where the convoy was headed.
Both the Islamic State group and al-Qaeda have decided to focus on the Sahel region of Africa, after suffering setbacks in the Middle East.
The Sahel is a strip of semi-arid land beneath the Sahara Desert that stretches across the continent from east to west. It includes parts of Chad, Niger, Mali, Burkina Faso and Mauritania.
French troops have been trying to help the region's armies tackle militants since 2013.
In August French troops withdrew from Mali after a diplomatic fall-out with the country's military rulers, however, they remain in other Sahel countries.
There was concern from other African nations that France's Mali withdrawal could exacerbate the jihadist insurgence in the area.
"We will be obliged to increase our defence forces and increase the protection of our borders," Ivory Coast's President Alassane Ouattara said, warning it would create a political vacuum.
Ghana's President Nana Akufo-Addo has urged the UN to keep its peacekeeping force in Mali despite the French departure.