LAGOS, Dec. 20(Xinhuanet)-- Royal Dutch Shell on Tuesday closed two oilfields in Nigeria's oil-producing Niger Delta following a dynamite attack carried out by gunmen on a pipeline it operates, the company said in a statement.

"The SPDC(Shell Petroleum Development Co.) has shut in production from Diebu Creek and Nun River fields as well as all Land Area facilities except Rumuekpe. Some 170,000 bpd(barrels per day) net oil have been deferred," the statement said.

It said the closure was the aftermath of an explosion on a crude oil pipeline belonging to the SPDC across the Opobo Channel, 50 km south-west of the southern oil city of Port Harcourt in the early hours of Tuesday.

"Preliminary investigations reveal that the fire may have been caused by a dynamite attack carried out by unknown persons," it said. The sabotage resulted in a major spill and fire.

The pipeline explosion followed on from two other security incidents: an attack by unknown gunmen on a security post at Fisiokiri in its Cawthorne Channel field, and another attempted attack on a liquefied natural gas tugboat within the same period.

"The attackers and their motives are yet to be identified," said the statement.

"The number of affected communities is yet to be determined but we understand that some nearby settlements may have been impacted... we have mobilized a medical team that is now on standby in Port Harcourt."

Shell is the biggest player in Nigeria, accounting for almost half of the African top oil producer's daily exports of 2.5 million barrels. Enditem