Africa's vultures are increasingly the victims of poisoning and poachers, leaving around half the continent's 11 vulture species critically endangered, a top conservation body warned Thursday.

The International Union for the Conservation of Nature said six African species of the large scavager birds had become more threatened by extinction than a year earlier.

The birds, which mainly feed off the carcasses of dead animals, are falling victim to the widespread use of poisoned baits and that they are also hunted since their body parts, used in traditional medicine, the nature conservancy group said.

In addition, vultures are being deliberately targeted by poachers, who want to avoid having them alerting authorities to illegally killed big game carcasses, IUCN said.

In an update to its "Red List" of threatened species, the IUCN said that, according to an assessment by its partner BirdLife, four African vulture species have become critically endangered, including the hooded vulture and the white-backed vulture, while two others are now considered endangered.

Among the five other vulture species found in Africa, one had maintained its "endangered" status.

They are among 24 bird species worldwide classified as being either vulnerable, endangered or critically endangered, IUCN said.

Only two vulture species on the continent, the Griffon and the Palm-nut vultures were still in the "Least Concern" category, it said.

"As well as robbing the African skies of one of their most iconic and spectacular groups of birds, the rapid decline of the continent's vultures has profound consequences for its people, as vultures help stop the spread of diseases by cleaning up rotting carcasses," said Julius Arinaitwe, head of BirdLife International's Africa division.

The updated Red List showed a deteriorating situation for 40 bird species around the globe.

In addition to vultures, a range of wading shorebirds have become more at risk, as have iconic species such as the Helmeted Hornbill, Swift Parrot, Atlantic Puffin and European Turtle-dove, IUCN said.

Another 23 species have been downgraded to lower threat categories, in part due to conservation action, including the Seychelles Warbler and Chatham Petrel, it said.