An Amnesty report says that at least 9m barrels have leaked into the land and rivers in the past 50 years

Serious allegations of human rights abuses caused by oil companies in the Niger Delta, the oil-producing region in southern Nigeria, have been published today.

A 141-page report by Amnesty International quotes sources suggesting that in the last 50 years at least 9m barrels worth of oil have leaked into land and rivers in the region.

Royal Dutch Shell is singled out by Amnesty as the most powerful operator in the region. The report will make uncomfortable reading for the energy group's new chief executive, Peter Voser, who starts work tomorrow.

The report gives evidence of oil spill cover-ups, gas flaring near villages and waste dumping leading to serious pollution of wetlands and the destruction of farming and fishing. The Niger Delta is notorious for violence and gangs are often used as security forces by oil firms to prevent terrorist attacks, hijackings and assaults on oil installations. The region has become unstable, with Nigeria's military launching fierce attacks on villages to flush out suspected terrorists, but this has led to the displacement of thousands of people.

The Amnesty report lays the blame for the region's intractable problems on the oil industry. "Decades of pollution and environmental damage, caused by the oil industry, have resulted in violations of the right to an adequate standard of living, including food and water, violations of the right to gain a living through work and violations of the right to health," it says.

"A lack of accountability and the inability of those affected to access justice or receive adequate reparations and remedies, has perpetuated the context of human rights violations and encouraged them to occur again and again. So long as impunity for abuses of the environment and human rights remains entrenched, so too will the poverty and conflict that has scarred the Niger Delta."

Shell, which trades in Nigeria through the Shell Petroleum Development Company – a consortium which also includes the Nigerian government, Total and Agip – disputes much of the Amnesty report. It argues: "About 85% of the pollution from our operations comes from attacks and sabotage that also puts our staff's lives and human rights at risk."

Amnesty says oil firms treat communities as a "risk" instead of as stakeholders.