Col. Rabe Abubakar, Nigerian military's joint task force spokesman, said nine Filipinos and five Nigerians were released Saturday and four Ukranians were freed Sunday, CNN reported.
Nigeria's military last week began its first major operation against the Movement for the Emancipation of the Niger Delta, an armed militant group that demands better distribution of the country's oil wealth.
Military and militants said the fighting resulted in a high number of casualties, with death toll estimates reaching up to 1,000, said Victor Burubo, a spokesman for the Ijaw National Council, which represents the region's largest ethnic group.
Fighting has destroyed four villages near the militants' camps , Burubo said. However, Abubakar said Nigerian forces aren't targeting civilians, blaming the attacks on the militants.
"We are not attacking villages -- just (militant) camps," Abubakar said.
The militants said last week the military conducted "indiscriminate aerial bombardment on the defenseless civilians," punishing the area for the "humiliating defeat" of the army in raids on two militant camps.