Gunmen in Nigeria's troubled oil-rich southern Rivers state have set free a Nigerian oil worker and a Pakistani construction manager seized about a month ago.  Gilbert da Costa in Abuja reports that only one hostage is being held in the volatile state.

Militants wearing black masks, military fatigues and carrying Kalashnikov assault rifles and rocket-propelled grenade launchers patrol the creeks of the Niger Delta area of Nigeria (File)

"If it is the Pakistani engineer you are talking about, Engineer Mohammed, they just dumped him somewhere and the man found his way to one of my police stations in that Ogoni area, and the police handed him over to his employer," he said.  "But there is still one hostage left, a Briton.  He is the only one left.  When they hold them and nobody is coming forward they will bring them out.  Because it is no longer business as usual."
 
Peter Agwuna, a Nigerian supervisor with the Elf oil company was kidnapped on his way to church on August 1, and was released late Monday.  His release came a few hours after a Pakistani construction manager was set free by his abductors, one month after he was kidnapped.
 
Violence in Nigeria's oil heartland increased sharply last year when armed groups started blowing up oil facilities and kidnapping foreign workers to protest what they called neglect and corruption in the impoverished delta.
 
More than 200 foreigners, mostly oil workers, have been kidnapped in the region since the start of 2006.
 
Most have been released after the payment of ransom.  The relatives of wealthy locals have also been the target of hostage-takers.
 
The violence has forced the closure of several oil fields, cutting Nigeria's oil output by as much as one-fifth.