(Adds details, background) By Felix Onuah ABUJA, June 24 (Reuters) - A senior U.N. official appointed by Nigeria to help end unrest in the oil-producing Niger Delta said on Tuesday he would seek a 90-day truce with militants as a first step towards formal peace talks. Ibrahim Gambari, a former Nigerian foreign minister who is a special adviser to U.N. Secretary-General Ban Ki-moon, was appointed by President Umaru Yar'Adua to prepare a long-awaited summit meant to address the root causes of the violence. The bombing of pipelines and kidnapping of oil workers in the Niger Delta, whose oil output makes Nigeria the world's eighth biggest exporter, have cut production by a fifth since early 2006, helping to push world oil prices to record highs. "We will hold thorough consultations in the creeks with the militants and stakeholders in the Niger Delta so that we can have a truce that will last for at least 90 days to create an atmosphere for the summit," Gambari said after meeting Yar'Adua. "This summit will be different from the others. It will be a comprehensive approach to the problems of the Niger Delta," he said, speaking publicly for the first time since his appointment. Gambari said Yar'Adua would announce more details soon on the venue and the date for the summit, first scheduled to be held almost a year ago. The president said earlier this month that it would take place in July. Five decades of oil extraction by international firms have polluted the land and water of the Niger Delta, a network of swampy creeks in southern Nigeria. Villagers live in abject poverty while corrupt politicians and criminal gangs grow rich from a lucrative trade in stolen crude, complicating efforts to pacify the region. SPLINTER GROUPS Yar'Adua came to power just over a year ago promising to engage the Niger Delta militants, but the peace process has made little real progress since then. The main militant group, the Movement for the Emancipation of the Niger Delta (MEND), carried out its most daring attack to date on Thursday, forcing Royal Dutch Shell <RDSa.L> to shut production at Bonga, its main Nigerian offshore oilfield. MEND announced a unilateral ceasefire on Sunday but has stopped short of agreeing to participate in the peace summit, saying it will only do so if Henry Okah -- one of its leaders on trial for treason and gun-running -- is allowed to attend. Another group -- the Ijaw Youth Council, which has held talks with the government in the past -- has also said it will not take part. Some analysts doubt the summit will achieve much given the fragmented nature of the militants and the lack of a cohesive strategy among Nigeria's federal, state and local governments. Previous attempts at peace talks have had little impact. "From what the president told me, our steering committee is going to be given a free hand and will be independent ... Our committee will focus on analysing the previous efforts, why they failed," Gambari said. The Movement for the Restoration of Niger Delta Struggle (MORNDS), a little-known group which claimed it was behind an attack on a Shell pipeline at Awoba in the delta last month, added its voice to the list of sceptics on Tuesday. "(We) implore our elders and every other stakeholder in the region to steer clear of the inglorious and discredited summit ... The Niger Delta people want implementation and not summits anymore," it said in a statement. (Writing and additional reporting by Nick Tattersall; Editing by Randy Fabi)
