The report contradicts the commander of a military task force, who said only one person was killed in the raid last Saturday on the village of Odioama, aimed at flushing out a group suspected of killing civilians and stealing crude oil.
Reporters visiting the village saw about 50 houses burned or collapsed and said most residents had fled.
"At last count, 14 persons have been buried," said Odioama youth leader Ruben Diepreye.
The military launched the attack in response to the killing of 12 people, including four local councilors in early February in a boat ambush by armed men embroiled in a bitter dispute over an oil-rich parcel of land.
But Odioama residents said the surprise raid by army and navy appeared to target civilians.
"It's just a genocidal campaign against me and my people," said Cadbury Omiey, the traditional ruler of the village.
The wetlands of the Niger Delta in southern Nigeria produce almost all of the OPEC member nation's 2.3 million barrels per day of oil.
Tensions have been high in the fishing community since energy giant Royal Dutch Shell started developing an oilfield at Obioku, which has been claimed by rival communities in the Odioama area.
Nigeria's military has been criticised for using excessive force in previous attacks on communities in the Niger Delta, where the government has deployed thousands of troops to protect oil installations operated by foreign multinationals.
Industry officials estimate about 10% of Nigerian crude oil is stolen and sold on international market.