LAGOS (Reuters) - Nigerias main rebel group said on Monday it sabotaged an oil tanker loading dock in Lagos state, killing five people in the first attack outside the Niger Delta since the group began its latest spate of violence. The attack comes as the government prepares to release Henry Okah, the suspected leader of the Movement for the Emancipation of the Niger Delta (MEND), after more than a year in detention for suspected arms dealing. MEND said its fighters set loading tankers and the depot ablaze overnight at the Atlas Cove Jetty in Lagos, a key port where vessels offload gasoline, diesel and other products from refineries in the southeast of Africas biggest oil producer. Heavily armed MEND fighters (on Sunday) ... carried out an unprecedented attack on the Atlas Cove Jetty in Lagos state, the militant group said in a statement. The fire killed at least five people and damaged pipelines and the terminal, which was shut down for repairs, said Capt. Geoffrey Boukoru, who led rescue efforts. MEND has rarely attacked sites outside the Niger Delta, focusing mainly on oil facilities in the Delta, Bayelsa and Rivers states in southern Nigeria. They are obviously getting much bolder, said a private security source working for the oil industry. We are on the look out for more attacks. They could happen anywhere now. The militant group has claimed a series of attacks against the oil industry following the militarys largest offensive in the Niger Delta for years in late May. The violence has forced Royal Dutch Shell, US oil company Chevron and Italys Agip to shut down around 300,000 barrels per day of production in the last seven weeks, lifting global oil prices. REBEL LEADER President Umaru YarAdua has offered a 60-day amnesty programme to gunmen in hopes of halting the unrest which has prevented Nigeria from pumping above two-thirds of its installed capacity since early 2006, costing it billions of dollars in lost revenue. MENDs Okah, on trial for gun-running and treason, has accepted the amnesty programme and is expected to be released early this week, his lawyer said on Sunday. Okahs release has been one of the main demands for MEND, a loose faction of rebel groups who say they are fighting for a fairer share of the regions oil wealth. MEND says it will continue its attacks even if it begins peace talks with the government. The militant group has repeatedly dismissed the amnesty programme in its current form, but said it was open to negotiations with the government. Although some militants have said they would lay down their arms on Okahs release, analysts believe violence will persist. Oil theft is a lucrative business in the region and politicians would continue to hire armed gangs to secure power in the run-up to 2011 elections, analysts said.