(Updates with new details on hostages held by MEND) By Austin Ekeinde PORT HARCOURT, Nigeria, June 1 (Reuters) - Gunmen used dynamite and heavy machine guns to kidnap at least three senior managers of Indonesian chemical company Indorama in Nigeria's southern oil-producing Niger Delta, police said on Friday. In a different area of the impoverished delta, community elders expelled protesters occupying a major oil export pipeline hub and reopened valves to allow crude oil to flow. The pre-dawn raid by suspected ransom-seekers on Indorama's residential estate in Rivers state added to a tally of 20 foreign workers being held by various armed groups in the delta, home to Africa's largest oil industry. Six of the hostages have been held since May 1 by the rebel Movement for the Emancipation of the Niger Delta (MEND), which had promised to free them on May 30 but has yet to do so. "We are worried for the safety of the hostages. The Nigerian soldiers shoot at anything that moves. We would not want them killed by the Nigerian military. They are being held deep in the creeks and it's a long boat ride to civilisation," the MEND spokesman said in an email to Reuters. The spokesman, who uses the pseudonym Jomo Gbomo, said he had asked Chevron <CVX.N> to provide a helicopter to free the four Italians, one American and one Croat, but the oil firm had refused. The six were seized from a Chevron offshore oil rig. Most hostages in the Niger Delta are released unharmed in exchange for ransoms, though two were killed last year in botched attempts to free them by Nigerian security forces. PROTEST At Indorama, police said three managers were kidnapped, a security source said four, while a union leader said five. Thousands of Indorama workers used trucks and vans to blockade a major road leading out of the Rivers state capital Port Harcourt to protest against the abductions. "We cannot continue to tolerate this nonsense," said Kris Natty, chairman of the Indorama workers' union. Violence in the Niger Delta stems from a complex set of factors including poverty, lack of basic services, corruption among government officials and security forces, resentment towards foreign oil companies and political thuggery. President Umaru Yar'Adua, who was sworn in on Tuesday, will host a summit with politicians and other delta representatives in the capital Abuja on Monday to tackle the crisis. Former President Olusegun Obasanjo held a series of similar summits last year which failed to stop an upsurge of violence that has killed dozens of people and forced the closure of more than a quarter of Nigeria's oil production capacity. The supply disruptions in the world's eighth-biggest oil exporter have pushed up prices on international markets. The shortfall in Nigerian oil output currently stands at over 900,000 barrels per day (bpd). In the Ogoni area of Rivers, Royal Dutch Shell <RDSa.L> had been forced to reduce output by 150,000 bpd since Tuesday because of the occupation of the Bomu pipeline hub by protesters demanding money or contracts from the oil major. About 100 members of the nearby K-Dere community, including traditional chiefs, chased them away on Friday morning. "We can't tolerate that behaviour. We are at the manifold and the valves are open," Blessing Kolzor, chairman of the K-Dere council of chiefs, told Reuters at the site. Shell was not immediately available to comment. (Additional reporting by Tom Ashby in Lagos and Estelle Shirbon in Abuja))
