The Senegalese army has launched an offensive against rebels in the southern Casamance region, after 16 villagers had their left ears cut off.
A military spokesman said the operation was aimed at protecting villagers from attack during the cashew-nut harvest.
The MFDC rebel group, which has waged a long separatist campaign in the region, has denied links to the mutilations.
Senegalese human rights groups say the attack threatens the relative calm in the area in recent months.
"The operations are still under way. We need to protect the villagers who are busy harvesting cashew nuts, so that they can continue safely their activities," Commander Prosper Basse told the BBC.
The cashew-nut harvest time has regularly seen an upsurge in violence and armed attacks. Cashew nuts are one of the area's main cash crops.
"These are awful attacks and we can't tolerate them," the army spokesman said.
He did not indicate if any arrests had been made.
Local media say the offensive is targeting rebel bases near the border with Guinea-Bissau.
The Movement of Democratic Forces of Casamance (MFDC) has condemned the attack as "barbarous".
"Our interest is to maintain calm until we can sit down with the government of Senegal and bring definitive peace to Casamance. We do not want civilians to be targeted," said the MFDC's Antoine Diamacoune.
This is the first case of such deliberate mutilation during the region's 26 years of conflict.
Lansana Manga, 31, said they were harvesting the nuts in Niaguis, 20km from the regional capital, Ziguinchor, when they were approached by men dressed in military fatigues and armed with rifles.
"They tied our hands before cutting off one ear each," he told the AFP news agency.
"They said it was to punish us because we were in their territory."
The National Human Rights Organisation has demanded that the perpetrators be found and charged with crimes against humanity.
The African Alliance for the Defence of Human Rights - another Dakar-based group, earlier involved in mediation efforts between the government and the MFDC - also expressed concern.
It said the mutilation may put an end to the relative lull which has prevailed in the province for the past few months.
A peace deal was signed with the main MFDC faction in 2004 but armed robbery remains common in the area, badly hitting its once vibrant tourist industry.
The Gambia lies between Casamance and the rest of Senegal and the MFDC rebels started a war for independence in 1982.