The Trump administration has ended federal research using human foetal tissue, delivering a victory to anti-abortion advocates.
The move, announced on Wednesday, has been criticised by scientists who say such tissue is essential in researching diseases like HIV and cancer.
The Department of Health and Human Services cited "the dignity of human life" as a "top priority".
Privately funded or university-led research is not affected by the policy.
"Promoting the dignity of human life from conception to natural death is one of the very top priorities of President Trump's administration," the department said in a statement.
Any National Institutes of Health (NIH) research that requires acquiring new foetal tissue will no longer be conducted under the policy change.
As for external grant applications that would use this tissue, HHS said they will be subject to review from an ethics advisory board to determine "whether, in light of the ethical considerations, NIH should fund the research project".
In 2018, the Department of Health and Human Services (HHS) began reviewing all federal research involving human foetal tissue and halted any new acquisition of tissue.
Now, the government will also not renew a $2m (£1.5m) contract with the University of California San Francisco (UCSF) for research using tissue from elective abortions. The contract expires on 5 June.
"The audit and review helped inform the policy process that led to the administration's decision to let the contract with UCSF expire and to discontinue intramural research - research conducted within the National Institutes of Health - involving the use of human foetal tissue from elective abortion," the statement said.
According to the Associated Press, a senior official said the policy move came from President Donald Trump, not the NIH Director, Francis Collins.
Mr Trump has been outspoken about his anti-abortion views during his presidency.
The official said the changes would affect at least three active federal projects and as many as 12.
Cell lines created from human foetal tissue have been instrumental in developing treatments for diseases from arthritis to cystic fibrosis and vaccines for rubella, adenovirus, rabies, chickenpox and polio.
Scientists say it is also the only way to develop a cure for HIV, the Zika virus and childhood cancers.
In a surprise ruling last month, the US Supreme Court upheld a state requirement that all foetal remains - whether from miscarriage or abortion - be buried or cremated.
Lawmakers and activists have begun to weigh in on the controversial policy.
"There is never a time that a child wasn't a child," Oklahoma Senator James Lankford, a Republican, tweeted.
As a nation, we demand transparency & humanity when other human organs & tissue are donated for research or life-saving operations. It’s reasonable to have the same integrity and ethical process for the use of human fetal tissue.— Sen. James Lankford (@SenatorLankford) June 5, 2019
The March for Life, an anti-abortion organisation, applauded the decision, saying: "This type of research involves the gross violation of basic human rights and certainly, the government has no business funding it."
Democratic congresswoman Lois Frankel of Florida said the US was "heading back to the dark ages".
We're heading back to the dark ages! By restricting fetal-tissue research, the Trump Admin is undermining critical, life-saving care for HIV, Parkinson's, Zika & more. This war on women & access to quality, affordable health care must stop! https://t.co/rwO1xNcA5P— Rep. Lois Frankel (@RepLoisFrankel) June 5, 2019
Fellow Democratic congresswoman Diana DeGette called the measure "chilling" and said it "only prevents the discovery of even more breakthroughs in the future".