The US government has decided to end its support for all biomedical research on chimpanzees.

Francis Collins, head of the US National Institutes of Health (NIH), said that his agency will no longer maintain its last colony of 50 chimpanzees for future research.

The move came more than two years after the NIH decided to retire all but 50 of its chimpanzees to animal sanctuaries.

In June 2013, the NIH announced it would significantly reduce the use of chimpanzees in agency-supported biomedical research and retain only 50 chimpanzees in case they were needed in the future.

However, "no new biomedical research projects have been approved" since then, Collins said in a statement released on Wednesday.

Another development was that the US Fish and Wildlife Service announced this summer that it has designated captive chimpanzees as endangered. That means researchers should apply for and obtain a permit to use captive chimpanzees in research if it could harm the animal.

"Up to this point, we are not aware of any permits that have been sought for this purpose," said the NIH director.

As a result of these numerous changes over the last few years, "it is clear that we've reached a tipping point," Collins concluded.

He said the remaining 50 chimpanzees will be moved to the Federal Sanctuary System, operated by Chimp Haven in the state of Louisiana, as soon as space is available for them.

Collins stressed that the decision is specific to chimpanzees. "Research with other non-human primates will continue to be valued, supported, and conducted by the NIH," he added.