By Tife Owolabi

YENAGOA, Nigeria (Reuters) – Crude oil production at Nigeria’s Warri refinery in the country’s restive Niger Delta region has not been affected by an explosion heard near the site, the country’s oil labour union said on Friday.

The explosion heard by locals late on Thursday follows a series of attacks on oil and gas facilities in the Niger Delta by militants that have cut the OPEC member’s crude oil production by about a third.

“No one has been able to pinpoint the explosion but there was a big bang around Warri axis yesterday. For now no production is affected,” said Cogent Ojobor, zonal chairman of the Nigeria Union of Petroleum and Natural Gas Workers (NUPENG).

The Nigerian navy said the blast was caused when its officers foiled an attempt to attack energy facilities.

“Our men fired at a boat that was suspected of carrying explosive materials,” said navy spokesman Joseph Dzunve, adding that the gunfire was likely to have hit the explosives.

In a separate incident in the Niger Delta on Thursday, a Nigerian militant group claimed responsibility for an attack on the Unenurhie-Evwreni pipeline in Ughelli.

(Writing by Alexis Akwagyiram; Editing by Susan Fenton and David Goodman)