Seven people have been found dead in Rio de Janeiro's port after what police said was a deadly clash among suspected drug dealers.

Military Police arrested 13 people and seized 14 guns, grenades and ammunition, they said.

Suspects were taken to a detention center while police rolled out in force in the area where it happened, called Complexo do Caju.

The suspects were involved in a shootout among themselves, military police said, adding that city police would determine who was firing on whom.

Violent crime is a major issue in Brazil, and especially in Rio, the former Olympic and World Cup host city.