Kidnappers freed four more foreign oil-worker hostages Tuesday in Nigeria, police said.

The two Ukrainians and two Norwegians snatched by gunmen last week were handed over to authorities in the southern oil center of Port Harcourt, Bayelsa State Police Commissioner Hafiz Ringim said by telephone.

Nigeria's oil-rich southeastern delta has seen 14 abductions in the last week. Kidnappings and sabotage attacks by militants, who argue that the impoverished region does not benefit from its oil, have cut Nigerian production by more than 20 percent since the beginning of the year. Most kidnap victims in the delta are returned unharmed.