Nigeria's main militant group says it has blown up two more oil pipelines in an overnight attack. Militant attacks repeatedly force oil companies to cut production in Nigeria, pushing up oil prices on international markets. Sarah Simpson has more from Lagos.

In an email to journalists giving details of the overnight attack, the Movement for the Emancipation of the Niger Delta says the pipelines in Rivers State are operated by a unit of oil giant Royal Dutch Shell PLC.

Shell spokeswoman Caroline Wittgen in Nigeria confirmed to VOA that an incident had taken place. However she could not provide any further details until an assessment had been made of the site from the air.

Last week MEND said a ceasefire, called in June, was over and threatened fresh attacks on the oil industry.

MEND wants a greater share of Nigeria's oil wealth to benefit the Niger Delta, which produces the country's vast oil exports. The people of the delta are desperately poor despite the riches beneath their land.

The militant group also wants Henry Okah, one of its leaders, released from Nigerian detention. Okah faces a number of charges, including treason, which carries a possible death penalty.

In recent years, MEND attacks have targeted oil infrastructure and forced Nigerian oil production to drop by some 25 percent.

Nigeria is the largest oil producer in Africa and a key exporter of crude to the United States.

Militant attacks and the kidnapping of foreign workers in the region have contributed to record high crude oil prices.