Nigerian militants who say they have kidnapped four foreign oil workers and attacked a Shell oil platform claim to have carried out more raids.
Gunmen attacked an oil installation over the weekend
The group says it attacked platforms run by the Total and Agip oil firms. Both companies have denied the claims.
The increased tension in the Niger Delta region has pushed up oil prices to more than $67 (£38) a barrel.
The four foreign workers, who are said to be in good health, have been held hostage for close to a week.
President Olusegun Obasanjo has appealed to the kidnappers to "not to do anything that might result in the loss of lives" and has set up a committee to work for their "prompt release".
In a statement, the previously unknown rebel group, the Movement for the Emancipation of the Niger Delta, said its ultimate aim was "to prevent Nigeria from exporting oil".
The group want local Ijaw people to benefit more from the region's oil wealth and are demanding the release of separatist leader Mujahid Dokubu Asari, being held on treason charges, by Friday.
"We will attack all oil companies, including Chevron facilities," it said. "Pipelines, loading points, export tankers, tank farms, refined petroleum depots, landing strips and residences of employees of these companies can expect to be attacked."
"We know where they live, shop and where the children go to school," it added.
The group attacked a Royal Dutch Shell pumping station near the port of Warri over the weekend, prompting the oil giant to withdraw some 330 workers.
One catering contractor died and 10 Shell workers were injured in the attack. An army spokesman said five soldiers were killed and nine were missing.
On Tuesday, President Obasanjo met high-level security chiefs and political leaders in an effort to halt attacks on oil facilities and to secure the release of the oil workers.
"A small committee has been set up to procure a political solution to the problem there. It's better to get to the underlying causes for the crisis, rather than engaging in any confrontation," Information Minister Frank Nweke told the BBC's Focus on Africa programme.
But military forces have deployed in strength on the waterways of the Niger Delta, prompting fears of further violence, AFP reports.
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.
Mr Nweke confirmed that the security forces had been in touch with the kidnappers and the four hostages, who come from the UK, the US, Honduras and Bulgaria, were well.
In a telephone call to the Reuters news agency, a man identifying himself as US citizen Patrick Landry said "these people are treating me good, but the climate is not what it should be".
A man who said he was Briton Nigel Watson-Clark said the kidnappers were demanding local control of the region's oil wealth, compensation money for pollution and the release of a separatist leader and an ethnic Ijaw militant.
The kidnappings are the latest in a string of violent incidents in the troubled region.