Over 400 plants and animals were added Wednesday to the "Red List" of species threatened with extinction, the authors of a new report said.

Of the 20,219 species now on the list, 4,088 are critically endangered, said the International Union for Conservation of Nature (IUCN).

Nearly 6,000 others were considered endangered, and more than 10,000 species were listed as vulnerable.

Two invertebrates, including a freshwater, air-breathing snail called Little Flat-Top, moved into the extinct category since the last "Red List" was published in June, said the IUCN.

The report, normally updated twice a year, was released on the sidelines of a meeting in India of parties to the UN's Convention on Biodiversity.

IUCN global director for biodiversity conservation, Jane Smart, said 25 percent of the world's mammals, 13 percent of its birds and 41 percent of amphibians were at risk of extinction.

"The figures are going up," she told journalists.