The US government said Wednesday it will send most of its 360 research chimpanzees into retirement but will keep a small colony of about 50 for possible future studies on vaccines and behavior.

The National Institutes of Health announced after more than two years of examination it was accepting most of the recommendations of independent experts to phase out the bulk of biomedical research using the primates.

The remaining 50 will not be bred, and may be used for research on creating a hepatitis C vaccine and for study of behavior and psychology, NIH director Francis Collins said.

"NIH plans to significantly reduce the use of chimpanzees in NIH-funded biomedical research," he told reporters.

"The majority of NIH-owned chimpanzees are expected therefore to be designated for retirement."

One recommendation the NIH did not accept was that chimpanzees should be provided at least 1,000 square feet (93 square meters) per animal.

Collins said there was presently not enough data to support that requirement, but that more study would be given to the matter.

The decision on retiring chimps will be implemented over the coming months and years, Collins said, describing chimps as "special animals" and "our closest relatives."

About 310 chimps in total will be designated for retirement, while another 50 will be kept apart for the research colony. The decision to keep those animals for research will be revisited in about five years, Collins said.

The NIH decision was applauded by animal rights groups.

"This is an historic moment and major turning point for chimpanzees in laboratories -- some who have been languishing in concrete housing for over 50 years," said Wayne Pacelle, president of The Humane Society of the United States.

"It is crucial now to ensure that the release of hundreds of chimpanzees to sanctuary becomes a reality, and we look forward to working with NIH and the sanctuary community to make that happen."

In 2011, the Institute of Medicine called for research on the great apes to continue only if there is no other model available, the research could not be performed ethically on humans, and it would hinder progress against life-threatening conditions if halted.

"The committee concludes that while the chimpanzee has been a valuable animal model in the past, most current biomedical research use of chimpanzees is not necessary," the IOM said at the time.

Chimps may still be necessary in the development of vaccines against hepatitis C, for short-term continued study of monoclonal antibody research against bacteria and viruses, comparative genome studies and behavioral research, it said.

The IOM is a respected group of medical experts that advises decision-makers and the public on matters of health and policy. Its recommendations were the first uniform set of criteria to judge the necessity of chimps in NIH-funded biomedical and behavioral research.

Earlier this year, an NIH-commissioned working group offered 28 recommendations on how to best ensure chimps were used as test subjects only when absolutely necessary.

NIH projects using chimps are already rare: of the 94,000 NIH-funded projects in 2011, only 53 used the primates.