Liberia's agriculture minister said that caterpillars infesting villages, destroying crops and threatening food security of an estimated 350,000 people were of the Achaea catocaloides species.

The species has attacked cocoa trees in other countries in West Africa, which supplies more than half the world's cocoa.

The caterpillars was previously thought to be the destructive "army worm" moth caterpillars, which had worried farmers in neighbouring Ivory Coast, the world's top cocoa grower.

"They are primarily forest insects that feed on trees, such as the Dahoma. The insect population can develop in large numbers and then attack agricultural crops," Agriculture Minister Chris Toe told reporters in the capital Monrovia.

Liberia, devastated by over a decade of civil war that ended in 2003, declared a national state of emergency last week after caterpillars were reported to have infested more than 100 villages, including several over the border in Guinea.

Guinea exports agricultural crops to Liberia, supplying much of the staples eaten in Liberia's capital Monrovia.

The UN Food and Agriculture Organisation said last week the insects, then thought to be army worms which are known to ravage crops, threatened to spread across West Africa.

The insects have caused panic in some villages, contaminating water supplies with their faeces, the FAO said.

Dr Toe said the Nigeria-based International Institute for Tropical Agriculture, as well as laboratories in Britain and elsewhere, had helped identify the species.