YENAGOA, Nigeria (Reuters) - Three people were killed and several wounded when an oil pipeline belonging to Italy’s ENI exploded during repair works in Nigeria’s southern Delta region, an environmental group said on Tuesday.

The blast was one of the worst in recent weeks in the swampland, where residents and former militant groups have long complained about oil pollution and casualties caused by pipeline accidents.

The explosion happened in the Olugboboro community in Bayelsa state on Sunday but bodies were only recovered on Monday after the fire was brought under control, residents said. Up to seven had been wounded, they said.

“The news of another tragic incident in the oil industry which claimed three lives ... came to the Environmental Rights Action (ERA) as a great shock,” said Alagoa Morris, an activist at the group.

“We in ERA will not stop calling on the authorities and regulators of the oil industry to make safety and best practices the mantra of the industry, not just profit (seeking),” he said.

The group and residents said workers had been repairing the pipeline when it caught fire. There was no immediate comment from ENI.

Several bodies had been burned beyond recognition, while some injured were brought with severe burns to hospitals, residents said.

Peter Idabor, director general of the National Oil Spill Detection and Response Agency in charge of handling spills and other pipeline accidents, said safety procedures had been breached during the repair works.

“I am going to report the matter officially to the Minister of Environment today,” Idabor said.

Tensions have been building in the Delta, an impoverished region where most complain they do not benefit from oil production.

Pipeline attacks by militants and other residents have been on the rise since authorities issued in January an arrest warrant for a former militant leader for corruption charges.

In 2009, the OPEC member brokered a multi-million amnesty for militants who ended blowing up pipelines to demand a greater share of the country’s oil wealth and an end of oil pollution.

President Muhammadu Buhari, elected a year ago, has extended the amnesty, but upset former militant leaders by ending generous pipeline protection contracts.