The Shell Petroleum Development Company of Nigera Ltd., or Shell Nigeria, says efforts to clean up the country's river deltas, which have witnessed severe oil spills in recent years, are being hampered by sabotage and theft.

Amnesty International pressured the African subsidiary of Royal Dutch Shell this week to dedicate $1 billion to clean up two oil spills that damaged the delta's farmland and waterways near the town of Bodo outside Port Harcourt in 2008.

The human rights group claims, in a recent report, a fault in the Trans-Niger pipeline released anywhere up to 1,640 to 4,000 barrels a day into the local swamp land for as long as four to 10 weeks. The spill was eventually stopped on Nov. 7, 2008. A month later, the pipeline sprung another leak in the same area, and it took crews another 10 weeks to stop the flow of oil.

If estimates are correct, the 2008 oil spills in the delta are larger than the Exxon Valdez spill that polluted Alaska in 1989. The group says in its report the damage done to the country's environment is so extensive losses in vegetation can be seen from space.

Amnesty's report follows an earlier environmental impact report conducted by the U.N. Environment Programme published in August, which pointed to oil-contaminated areas of the country's coast..

Shell Nigeria, on its website, wrote a promise to reevaluate areas of the country affected by oil spills, but Shell officials blamed the spills on oil thieves - as many as 16 reported thefts in September alone.

We are very disappointed that oil thieves are still at work, Tony Attah, vice president of Shell Sub-Saharan Africa,said. This is why we call for concerted efforts to help stop this criminal activity which not only puts the lives of the perpetrators and the public at risk, but causes severe environmental impact and impacts the communities in the area.

In the company's official responce to Amnesty International, a spokesperson for Shell Nigeria said the company has publicly acknowledged and taken responsibility for the 2008 spills which were a result of operational issues. But Shell Sub-Saharan Africa quickly noted the challenges the company faces in the region.

The reality is that our efforts to undertake cleanup in Bodo have been hampered by the repeated impact of sabotage and bunkering spills, company officials wrote in a statement. The United Nations Office on Drugs and Crime estimates that over 150,000 barrels of oil a day are stolen in the Niger Delta - that cannot be ignored.

If Amnesty really wanted to make a difference in the Niger Delta, it would join with us in calling for more action to address this criminal activity, which is responsible for the majority of spills, Shell officials wrote.