Chief Thomas Ekpemupolo, the 84-year-old father of rebel leader Government Ekpemupolo, died at a hospital in Warri from injuries sustained during military incursions into his community, Paul Bebenimibo, a spokesman for the son, known as Tompolo, said.
Tompolo was a commander of the Movement for the Emancipation of the Niger Delta (MEND), a group that spearheaded attacks on oil and gas installations in the Delta region in the early 2000s until a government amnesty program halted clashes by offering contracts to protect pipelines and oil production equipment.
A wave of attacks on oil and gas facilities kicked off not long after an arrest warrant was issued for Tompolo in January on charges of corruption.
Godspower Gbenekama, a community leader in Tompolo's home area, said doctors had tried in vain to save the father by amputating a leg.
"We have appealed for calm but it is very painful considering the circumstances that led to his death," he said.
"His leg was amputated because he could not gain immediate access to hospital and treatment after the injury because of the lock down after and during the period of the invasion," he said, referring to a search of his community by the army hunting Tompolo.
"By the time the military left our area it was too late," he said.
Comment from the government was not immediately available.
The violence has shut down more than 700,000 barrels per day of oil output and exacerbated an economic crisis in a nation reeling from its first recession in two decades. Tompolo has denied any involvement in the attacks on oil and gas infrastructure, as well as the corruption charges. He remains in hiding.
While oil minister Emmanuel Ibe Kachikwu said talks were progressing with militants over a ceasefire, the army is waging a campaign aimed at stamping out attackers. Locals have criticized the efforts as heavy handed, and said they risk fuelling more dissent, while other groups have said they run contrary to the ceasefire talks.
In a statement on Wednesday, the Niger Delta Avengers, the group that has claimed responsibility for bulk of the attacks this year, but recently declared a ceasefire, said the army campaign will "undermine any genuine disposition from your government toward restoration of tranquility in the Niger Delta."