Lagos (AFP) - Anglo-Dutch oil giant Shell said it re-opened on Wednesday two key supply pipelines in Nigeria shut last week because of leaks and sabotage that forced it to declare a "force majeure" on crude oil exports.

"The Shell Petroleum Development Company of Nigeria Ltd (SPDC)...today (September 2) lifted the force majeure on Bonny Light exports following the repair and re-opening of the Trans Niger Pipeline (TNP) and Nembe Creek Trunkline (NCTL.)", the company said in a statement.

The SPDC, a subsidiary of Shell in Nigeria, said it declared the force majeure last Thursday following the shutdown of both the TNP and NCTL.

The two pipelines take crude to the Bonny Light exports terminal, one of Nigeria's main oil terminals.

"Force majeure" is a legal term releasing a company from contractual obligations when faced with circumstances beyond its control.

Shell, a major oil operator in Nigeria, did not disclose the volume of output affected by the incident.

The company has blamed repeated oil thefts and sabotage of key pipelines as the major cause of spills and pollution in the oil-producing region.

Crude oil theft or "bunkering" is a major problem in Nigeria, with estimates that the country loses some $6 billion (4.3 billion euros) in revenue every year because of the practice.

In another development, the managing director of the state-run oil giant NNPC, Ibe Kachikwu, said Wednesday that the nation's armed forces would be involved in policing the nation's oil and fuel pipelines.

"Efforts are in top gear to fix all the crude and petroleum products pipelines across the country," an official Nigerian National Petroleum Corporation (NNPC) statement quoted him as saying.

"The Nigerian Airforce would be engaged to provide aerial survey of the pipelines, the Nigerian Army Engineering corps to fix and police the pipelines and the Nigerian Navy to provide marine surveillance for the network of pipelines," the statement said.

NNPC has more than 5,000 kilometres of pipelines across the country, some located in creeks and forests.

Kachikwu also said that ongoing phased rehabilitation of all the nation's four refineries -- expected to produce 20 million litres of petrol daily at full capacity -- would reduce petroleum products importation.

Nigeria is Africa's largest oil producer, accounting for more than two million barrels per day.