Local media reported five soldiers were killed, the British Broadcasting Corp. said Monday.
STV, a local television station, reported numerous people were hospitalized in the raid, and many weapons were stolen from the armory.
A spokesman for Renamo, a former rebel army movement and now an opposition political party, said he could not confirm the incident.
Renamo admitted attacking a police station in the region in April, the BBC said, adding Renamo and the governing Frelimo party fought each other during Mozambique's civil war, ending in 1992.
Notable deaths of 2014 [PHOTOS]