(Recasts with more quotes, background) By Austin Ekeinde PORT HARCOURT, Nigeria, Feb 3 (Reuters) - Nigeria's senior oil workers' union has threatened an indefinite strike from next Monday unless the government takes urgent steps to improve security in the Niger Delta after a surge in violent crime. Ethnic activists, oil workers and residents hardened by years of unrest have condemned the violence in the Niger Delta, saying it undermines any notion of political struggle by militants claiming to fight for the region's development. The strike threat issued on Tuesday by the PENGASSAN union came after gunmen killed an 11-year old Nigerian girl last week and abducted her 9-year old brother as they walked to school in the southern oil city of Port Harcourt. Their father works for oil giant Royal Dutch Shell <RDSa.L>. "We have given the government a 7-day ultimatum. We expect government to effectively improve security in the Niger Delta," PENGASSAN General Secretary Bayo Olowoshile told Reuters. "We are mobilising our members and engaging management on why our services should be withdrawn from all upstream facilities until security is improved in the region." He did not specify what measures the government or security forces must put in place before the union would lift its threat. Similar threats made by PENGASSAN over insecurity in the past were withdrawn after talks with the authorities and oil firms. There have been at least 10 attacks on vessels in the waters off the Niger Delta, home to Africa's biggest oil and gas industry, this year alone while criminal gangs have continued to kidnap prominent Nigerians and expatriates for ransom. The attack last Thursday, in which gunmen shot the girl as she tried to prevent them abducting her brother, shocked even long-suffering local residents. "Everybody knows that all these kidnappings are not part of the struggle for the development of the Niger Delta," said Christian Unagbo, a market trader in Port Harcourt. "What you are seeing today is the fallout of greed, a quest for quick riches ... It has nothing to do with agitation, rather it will make the genuine agitation of the people lose support." MILITANCY OR CRIMINALITY? The Movement for the Emancipation of the Niger Delta (MEND), the main militant group in the region which says kidnapping "high-value" European and North American oil workers is part of its strategy, ended a 5-month old ceasefire on Saturday. The group, whose campaign of sabotage against the oil industry has cut Nigeria's output by around a fifth over the past three years, warned of a "sweeping assault" on oil and gas installations after a military raid on one of its camps. MEND says it is fighting for a fairer share of the resources in the Niger Delta, where half a century of oil extraction has swollen government coffers and enriched foreign oil firms but left local villages mired in pollution and poverty. But the group, which is still holding two British oil workers seized five months ago, has struggled to distinguish itself from ransom-seeking criminal gangs. "Those Britons were taken as human shields to create a negotiating ground," said Chris Ekiyor, president of the ethnic rights organisation the Ijaw Youth Council. "What we have now, especially in Rivers state, are people who are just looking to make some quick money," he told Reuters. Some security experts say the rise in piracy and kidnappings in recent weeks has partly been triggered by low world oil prices making "bunkering" -- the local term for the theft of industrial quantities of crude oil -- less profitable. That has forced armed gangs to seek other sources of income. Local newspaper reports said PENGASSAN had written to President Umaru Yar'Adua over the worsening insecurity and held a meeting with the labour minister on Monday. (For full Reuters Africa coverage and to have your say on the top issues, visit: http://af.reuters.com/ ) (Additional reporting by Tume Ahemba in Lagos and Randy Fabi in Abuja; Writing by Nick Tattersall)
