Boko Haram is suspected of being behind the kidnapping of at least 20 people from a bus in Cameroon on Sunday, 12 of whom were executed.
The militants attacked a bus near Cameroon's northern border with Nigeria and kidnapped the passengers. Only 8 of the hostages have come out alive, locals said on Monday.
"The bus was coming from Koza and was travelling to Mora," a source told AFP, adding that all the survivors have since been released.
Cameroon, Chad, Nigeria and Niger have engaged thousands of their troops to take on the Islamist militants who have wreaked havoc in the region over the last year, killing more than 10,000 people and kidnapping scores of others.
Several of the jihadist fighters were killed in clashes with the Cameroon army in the village of Kerawa on Sunday.
Nigeria postponed its elections slated for 14 February to give its security forces the time to deal with the Boko Haram violence.