Palma and surrounding areas have been on tenterhooks since militants linked to the Islamic State launched a raid of unprecedented scale on the town, killing dozens and forcing tens of thousands to flee.
Many sought refuge in nearby Quitunda, a resettlement village next to a heavily guarded gas exploration site operated by French oil giant Total and abandoned days after the raid.
Several bouts of low-key violence have been reported since the militants retreated.
British charity Save the Children on Friday said it was “shocked and appalled” by news this week of two 15-year-old boys being beheaded in Palma on Sunday.
The teenagers were among a group of 15 adults who had left Quitunda in search of food, according to the independent news outlet Carta de Mocambique, which reported the incident.
Two adults were also killed, it added.
“We are appalled and disgusted at this senseless crime,” Save the Children Mozambique country director Chance Briggs said in a statement.
The insurgency is “having a continual, horrific, deadly impact on children,” he said.
“They are being killed, they are being abducted, they are being recruited for use by armed groups.”
One local source in the provincial capital Pemba said relatives in Quitunda had heard of “insurgents” beheading several people on Saturday.
Momade Bachir, who is regularly in touch with family members still stranded around Palma, told AFP that four residents were attacked after they left the town to pick manioc in surrounding fields.
Another three beheaded bodies were found near Pemba that evening, according to Bachir.
Finding food has been difficult since the March 24 attack on Palma and aid agencies have struggled to take in supplies due to security concerns.
The World Food Programme has warned that almost one million people, mostly displaced, faced severe hunger.
Insurgents have been wreaking havoc in Cabo Delgado since 2017.
The fighting has claimed more than 2,800 lives, half of them civilians, according to conflict data tracker ACLED, and displaced around 800,000.