A naval commander and three ratings were attacked and killed in the Channomi Creek near Warri while escorting a vessel carrying materials for Chevron's Escravos site.
The assailants hijacked the vessel but later released it along with the passengers.
Two explosions were alleged by local officials to have rocked pipelines at Clough Creek and the Nunn River operated by Agip near Twon Brass, causing spillage and forcing the oil company to cut supplies to the export terminal on Brass Island.
