An offshore oil facility operated by US oil group Chevron in southern Nigeria has been blown up, the navy said on Friday, in renewed violence that could hit exports in Africa's largest oil producer.

"Militants using explosives blew up the Okan platform, a collection facility for offshore oil and gas that feeds the Escravos terminal," navy spokesman Chris Ezekobe told AFP.

The attack, near Warri, in Delta state, happened on Wednesday night and was claimed by the Niger Delta Avengers group, he added.