Nigeria's main militant group has ended a three-month-old ceasefire in the Niger Delta, threatening "an all-out assault" on Africa's biggest oil and gas industry.

The Movement for the Emancipation of the Niger Delta (MEND) says it no longer trusts the government to negotiate demands for greater control of the region's natural resources. MEND is responsible for years of attacks on oil facilities to press its demands. It has also kidnapped numerous foreign oil workers.

The threat comes at a time when President Umaru Yar'Adua has been out of the country for more than two months. He has been receiving medical treatment in Saudi Arabia for a heart condition.

MEND rebels with foreign hostages (Photo: Flickr/ISN Security Watch/Dulue Mbachu)