Maputo - Mozambique on Thursday denied accusations by rights group Amnesty International that soldiers had committed atrocities, saying the acts were carried out by Islamist insurgents impersonating troops.

Militants with links to Islamic State have stepped up attacks in Mozambique this year, alarming governments across southern Africa.

Amnesty said on Wednesday it had seen videos showing soldiers in the uniforms of the Mozambique Armed Defence Forces and the Mozambique Rapid Intervention Police committing atrocities against alleged fighters in the northernmost province of Cabo Delgado."

The videos and pictures show the attempted beheading, torture and other ill-treatment of prisoners; the dismemberment of alleged opposition fighters; possible extrajudicial executions; and the transport and discarding of a large number of corpses into apparent mass graves," Amnesty said.

Mozambique's defence ministry on Thursday dismissed the report, saying militants regularly impersonated soldiers."

One of the tactics used by terrorists in their macabre incursions against the population is to pretend to be elements of the FDS (Defense and Security Forces) in a veiled attempt to confuse national and international public opinion," said ministry spokesman Colonel Omar Nala Saranga.

"The Defense and Security Forces reiterate that they do not agree with any form of torture, beheading attempts, mistreatment or illegal acts," he added in a statement.

Militant attacks began in Cabo Delgado in 2017, and have rapidly gathered pace this year with insurgents seizing key towns for brief periods and hitting military and other key targets.

The violence has alarmed energy majors exploring huge natural gas deposits there.