Security sources in north-east Nigeria say at least nine soldiers and two members of a civil defence militia have been killed by Islamist militants.
They told AFP news agency that several more civilians are missing, presumed killed or abducted.
The extremists used guns and grenades to ambush a civilian convoy of more than 100 vehicles under military escort near Damboa in Borno state - close to a forest enclave where Boko Haram militants have a base.
Their insurgency, characterised by frequent ambushes, has killed 36,000 people in a decade and spread to three neighbouring countries.
US condemns 'brazen killings' in northern Nigeria
The US has condemned the recent spate of "senseless and brazen killings" in northern Nigeria.
Days earlier some 20 people were killed and 20 injured during an attack in north-western state of Katsina by bandits who are often accused of involvement in cattle rustling and kidnapping for ransom.
"The US calls on the government of Nigeria to do more to strengthen ongoing efforts to address this violence, hold those responsible accountable and protect civilians," the US embassy said in a statement.
A decade-long insurgency in the north-east by Boko Haram Islamist militants, including a faction that fights under the banner of the Islamic State group, has left thousands of people dead and forced many more from their homes.
Deadly violence related to cattle has been going on for years in Nigeria - even longer than the northern Islamist insurgency and southern oil militancy.
In the past public such outbursts from soldiers have led to summons to a court-martial, so it is unusual for the military to respond saying the "uncomplimentary" remarks were due to "distress in the fog of war".