WARRI

Militants have released six foreign oil workers they deemed ”low value”, but held on to two Americans and one Briton and threatened crippling new attacks aimed at cutting off all oil production in Nigeria. American Macon Hawkins, who turned 69 on Wednesday, was the first to be released.

Nigerian authorities hunted for nine foreign workers being held as ”human shields” by rebel fighters on Tuesday as the crisis in Africa’s biggest oil industry forced world oil prices up sharply. The nine oilmen were seized on Saturday by separatist guerrillas during an attack on the energy giant Shell’s Forcados oil terminal.

Tension was mounting on Wednesday in the city of Warri as soldiers hunted for a heavily armed militia that has attacked oil facilities in southern Nigeria and kidnapped four foreign workers. Boat crews and human rights activists said military forces have deployed in strength on the waterways of the Niger Delta.

Ethnic militants vowed to prevent voting Saturday in a broad swathe of Nigeria’s oil delta during legislative elections that pose a test for civilian rule in Africa’s most populous nation.