Royal Dutch Shell shut the Trans Niger oil pipeline (TNP) after a fire, threatening to worsen a drop in Nigerian output due to unplanned disruptions, informed Business Report.

The TNP has been repeatedly attacked by vandals and oil thieves, and Shell said it would investigate whether the fire was the result of an attack by one of the armed groups that operate in the region, African Spotlight reported.

According to the company’s Spokesperson, Joseph Obari, fire has been observed on the right way of the TNP at Gio in Ogoni land.

The line transports natural gas and 180,000b/d of oil to an export terminal at Bonny, on the south coast.

Nigeria’s output dropped by 200,000b/d to reach 1.45mb/d in December 2016, ending three months of gains as the African nation struggled to restore capacity after a year of militant attacks on oil infrastructure.

In August 2016, production fell to 1.39m barrels, the lowest level since 1988.