In Mozambique's troubled province of Cabo Delgado, there have been 51 documented cases of minors being abducted - most of them young girls - over the past year, the charity group Save the Children reported on Wednesday.

The aid organization said the number was likely on the conservative side and that the true case count was probably "significantly higher" in the province, where Islamist terrorists have carried out a growing number of attacks since late March, DPA reported.

The abduction of children in Cabo Delgado is a "new and alarming tactic" by the militants and the hostages must be immediately released, Save the Children said.

Many of the children witness cruel attacks and are then abducted in whole groups, it said.

The population of oil-rich Cabo Delago has been suffering from brutal attacks for the past three years, but Islamist rebel groups have significantly expanded their attacks since late March.

Most recently, they attacked the northern Mozambican town of Palma on March 24. The Islamic State group took control of the city for several days, according to its own statements.