By Corinne Podger BBC science correspondent

Almost a quarter of the world's mammals face extinction within 30 years, according to a United Nations report on the state of the global environment.

Factors leading to mammals' extinction continue with "ever increasing intensity"

The destruction of habitats and the introduction of alien species from one part of the world to another are blamed for the threatened loss to biodiversity.

The United Nations Environment Programme (Unep) report is officially published on Wednesday. It identifies more than 11,000 endangered animal and plant species - including more than 1,000 mammals, nearly a quarter of the world's total.

One in eight bird species is also in danger of extinction, and more than 5,000 different plants.

Human encroachment

The species likely to vanish within three decades include well-publicised cases such as the black rhinoceros and the Siberian tiger, and less well-known animals such as the Philippine eagle and the Asian Amur leopard.

The UN report is a review of the past 30 years in terms of environmental damage.

Based on that assessment, the UN says that all the factors which have led to the extinction of species in recent decades continue to operate with "ever-increasing intensity".

The encroachment of human settlement into wilderness regions, rainforest and wetlands destruction, and the impact of industry, have had a dramatic impact on the survival of threatened animals and plants.

The report says many problems could be rectified if governments implement the treaties and conventions passed since the Rio Earth Summit in 1992.

These include the Kyoto Protocol on climate change and the Convention on Biodiversity.