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Niger Delta's peace broken by violence

1 May 2013 Last updated at 06:25 BST

It has been almost four years since an amnesty was given to thousands of militants who were causing havoc in Nigeria's oil-rich Niger Delta, but relative peace has recently been broken.

The peace allowed oil production in the region to soar, but the killing of 12 policemen has come as a warning that the peace may not be on solid ground.

Will Ross reports.