A top militant leader says that fighters have sabotaged two more oil pipelines in Nigeria.

The Movement for the Emancipation of the Niger Delta leader says Monday’s attack on two pipelines owned by a unit of Royal Dutch Shell PLC took place in Nigeria’s southern Rivers State.

The leader spoke to The Associated Press on condition of anonymity to avoid capture by authorities. Representatives of Shell in Nigeria weren’t immediately available for comment.

Such attacks have slashed this west African nation’s oil output by almost a quarter in the past two years, helping push world crude prices to historic highs.