Nigeria's main militant group said on Tuesday it had attacked a pipeline feeding the Warri oil refinery in the Niger Delta at the weekend. This is the latest in a string of attacks on Africa's biggest oil and gas industry.

"On Sunday, Nov. 21, 2010, at about 0200, fighters of the Movement for the Emancipation of the Niger Delta (MEND) attacked and destroyed the Obidi-Refinery trunk line," the group said in a statement sent by email.

State-run oil firm NNPC has said it is repairing damage to the Warri-Escravos oil pipeline but made no further comment on Tuesday.

The authorities have claimed significant victories over MEND in the Niger Delta in recent weeks. They freed 19 hostages held by the group and subsequently arrested the commander responsible and more than 60 of his followers.

But security experts have warned it is impossible to fully guard against attacks on the industry.

Oil infrastructure in the delta, a network of thousands of shallow creeks opening into the Gulf of Guinea, is extremely exposed. Thousands of kilometres (miles) of pipeline pass through remote and thickly forested terrain.

Disputes between local communities and oil firms are common, and attacking a pipeline and shutting down production requires little more than simple home-made explosives.

It is also extremely difficult to protect offshore platforms such as those operated by Exxon Mobil and Afren, from where 15 of the 19 hostages were kidnapped.

For such raids, the militants use open craft too small to be detected by radar. They are even able to operate far offshore by using a "mother ship", a larger vessel which supplies the speedboats with fuel and food, security experts say.

Source: Reuters