LONDON (Reuters) – ExxonMobil subsidiary Mobil Producing Nigeria has declared force majeure on exports of Nigeria’s Qua Iboe crude oil, the country’s largest export stream, a spokesman said on Friday.

The declaration came after the company observed a “system anomaly” during a routine check of its loading facility on July 14.

“We are working to ensure loading activities at the facility return to normal. We cannot speculate on any timeline for repairs,” the spokesman said. “Qua Iboe Terminal is operating and production activities continue.”

Nigeria has struggled to maintain its crude oil production following a spate of militant attacks and technical problems that in May pushed production briefly to 30-year lows. While the cause of the latest issue was not immediately clear, traders said it would take least two to four weeks to repair.

Earlier this week, Exxon denied claims from militant group the Niger Delta Avengers to have blown up the Qua Iboe 48″ crude oil export pipeline operated by the company.

Spokesman Todd Spitler said on Friday there was no connection between the force majeure and militant attacks.

Exxon has struggled to bring production of Qua Iboe back to normal after an accident in May on a drilling rig that damaged a pipeline, after which the company also declared force majeure.

Since lifting that declaration in early June, there have been roughly three revisions to loading schedules, attributed to a slower-than-expected resumption of flows, with loading delays of at least five days.

(Reporting by Libby George; editing by David Clarke and David Evans)