The bodies, which were cut into pieces, were left in Piqueue village, a local traditional leader told AFP, speaking on condition of anonymity.
“People were surprised while sleeping in the forest,” he said, indicating that the residents had fled the village for fear of being attacked.
The attackers also kidnapped four women, he said.
Mozambican police declined to comment, but a local army commander confirmed the attack.
“We urge people to stay in villages where they have protection from the police and the military,” he said.
Since October 2017, nearly 200 civilians, troops and police have died in a wave of violence in Cabo Delgado, a gas-rich northern region which borders Tanzania, with President Filipe Nyusi sending in troops to “neutralise” the Islamist threat.
This week, several hundred military personnel from 15 countries including the United States, Canada, Kenya and Madagascar completed a training exercise off the northern coast of Mozambique.
An annual maritime exercise, “Cutlass Express” aims to improve coordination against the drug smuggling, human trafficking and illegal fishing that allegedly funds extremists in East Africa and the Indian Ocean.
Bryan Hunt, deputy chief at the US embassy in Maputo, said the United States was ready to assist in quelling the Islamists.
“We are available and would like to help Mozambique fighting insurgent groups,” Hunt said this week.
“We already have several programmes in the maritime field and we would like to increase the level of cooperation between the two countries.”
The violence in northern Mozambique has raised concern among US energy firms seeking to drill major gas deposits off the coast.