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.
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