Nigerian militants who have kidnapped four foreign oil workers and attacked a Shell oil platform say they are preparing to carry out more raids.
Local people say they do not benefit from the oil wealth
The rebel group says it wants more control over the Niger Delta region's enormous oil wealth, and is demanding the release of two local leaders.
Negotiations between the government and the rebels are said to be continuing.
The foreign hostages have been captive for nine days and kidnappers say one of the men, an American, is very ill.
The hostages were allowed to speak by phone to the Reuters news agency on Thursday.
British hostage Nigel Watson-Clark said that all the men were suffering from diarrhoea and fatigue.
Mr Watson-Clark said they were being moved to different hiding places around creeks and swamps to avoid Nigerian army patrols.
The rebel group, the Movement for the Emancipation of the Niger Delta, is demanding the release of separatist leader Mujahid Dokubu Asari, being held on treason charges, as well as former governor Diepreye Alamieyeseigha, accused of corruption and money-laundering.
The previously unknown group has also reiterated a demand for compensation of $1.5bn from the Shell oil company for pollution in the region.
The group attacked a Royal Dutch Shell pumping station near the port of Warri last weekend, prompting the oil giant to withdraw 330 workers.
Oil workers' unions in Nigeria have threatened to withdraw members from the main oil-producing region unless the government moves to improve security.
The instability has led to a 10% fall in Nigeria's oil production. The country is Africa's leading oil exporter and the fifth-biggest source of US oil imports.
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