By Alex Kirby BBC News Online environment correspondent

It is a very serious situation indeed - it's a severe warning that we have no reason to say things are turning round

Achim Steiner IUCN

They are now classified by the International Union for the Conservation of Nature (IUCN) as critically endangered.

Its updated Red List of Threatened Species says more than 11,000 creatures now face extinction.

But two, an insect and a rodent, previously thought extinct, have been rediscovered.

Since the last edition of the list two years ago, over 400 new species have been assessed.

Dramatic decline

Of these, 124 have joined one of the threatened categories: critically endangered (CR), endangered (EN), or vulnerable (VU).

IUCN (also known as the World Conservation Union) says 11,167 species are now threatened with extinction, 121 more than in 2000.

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Saiga antelope: Extinct in one or two decades

One of the three species causing IUCN particular concern is the saiga, an antelope found in the deserts and steppes of central Asia.

It has suffered a major decline in the last decade, poached for both its meat and its horns, which are exported for use in traditional medicine.

In 1993 the total population was estimated at over one million: by 2000 this had fallen to fewer than 200,000. Scientists believe under 50,000 animals now remain in the wild.

Habitat fragmentation

IUCN's director general, Achim Steiner, told BBC News Online: "This rate of loss is unsustainable. If nothing is done, the saiga is doomed to extinction in one or two decades."

Another species, the wild Bactrian camel, is hunted partly because it competes with domestic camels and livestock for water and grazing, but also for sport.

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Lord Howe Island stick insect: Good news

Its main stronghold is China, where mining is destroying its habitat. Other problems include the effects of hybridisation with domestic camels, and increased human competition.

The plight of the third, the Iberian lynx, is dire: it may be the first wild cat to become extinct for at least 2,000 years. Fewer than half the 1,200 individuals recorded 10 years ago now survive.

The lynx lives in Mediterranean woodland, where habitat fragmentation by farming and industrial development means it now survives only in scattered groups in south-west Spain and Portugal.

Higher listing

The two species rediscovered after being listed as extinct are the Lord Howe Island stick insect, an Australian species, and the Bavarian pine vole, from Germany.

Other species of concern include:

• the Ethiopian water mouse (critically endangered), known from a single specimen found near a tributary of the Blue Nile in north-west Ethiopia - its habitat may be overgrazed by livestock
• the tiger tail seahorse (vulnerable) is caught for medicinal and aquarium uses, and accidentally as bycatch. Its habitat is also being degraded
• the slender-billed and Indian vultures are both classified as critically endangered because they have suffered extremely rapid population declines, particularly in south Asia. Suspected causes include disease, poisoning, pesticide use and changes in the processing of dead livestock.

IUCN has upgraded several species to a higher threat category, because it now judges them more vulnerable.

They include three birds: the Titicaca flightless grebe, the black-browed albatross, and the blue duck of New Zealand.

In 2000, 5,611 plants were assessed as threatened. With the addition of Mexican and Brazilian cactus assessments, the figure is now 5,714.

Wild Bactrian camel and day-old calf (Image: John Hare)

But with only about 4% of the world's described plants evaluated, IUCN says, the true percentage of threatened species is much higher.

The 2000 Red List said the extinction crisis was as bad as many people feared, with some "dramatic" population declines.

Achim Steiner told BBC News Online: "This update reaffirms the basic trends identified then.

"It is a very serious situation indeed - it's a severe warning that we have no reason to say things are turning round.

"The resources we have to compile the list are absolutely inadequate. It is people like birdwatchers and other nature lovers who generate an enormous amount of data voluntarily that are the heart and soul of the conservation movement.

"And there are the people in places like Africa who have no binoculars, but use wildlife every day. We count on them too."