Nigeria rebels claim more attacks: "Nigerian militants who say they have kidnapped four foreign oil workers and attacked on a Shell oil platform say they have carried out more attacks.

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.

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'.

'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 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.

Instability

The group attacked a Royal Dutch Shell pumping station near the port of Warri over the weekend, promp"