The White House pushed back on concerns expressed by the World Health Organization (WHO) after a US health official said a coronavirus vaccine might be authorized for use without completing full trials.
The White House also said that the United States would not join a global effort to develop, manufacture and distribute a coronavirus vaccine because of the WHO involvement.
About 172 countries are engaging with the WHO's Covid-19 vaccine plan to ensure equitable access to vaccines, known as COVAX.
"The United States will continue to engage our international partners to ensure we defeat this virus, but we will not be constrained by multilateral organizations influenced by the corrupt World Health Organization and China," White House spokesman Judd Deere said in a statement on Tuesday.
"This president will spare no expense to ensure that any new vaccine maintains our own FDA's gold standard for safety and efficacy, is thoroughly tested, and saves lives," he said, referring to the US Food and Drug Administration.
The global effort to develop a vaccine against the virus that has killed more than 858,000 people has seen recent launches of late-stage clinical trials, as work on treatments has also accelerated.
"It is disappointing that the US has decided not to join COVAX. The only way we're going to end this pandemic is if countries work together," Alex Harris, the Wellcome Trust health charity's Head of Global Policy, said in a statement.
"Economic recovery is not possible if large parts of the world are still shut down. The US will not be able to bounce back if its allies and trading partners are still suffering," Harris said.
The European Union on Wednesday opened the door for individual member states to buy vaccines through COVAX.
There is no approved coronavirus vaccine, except one authorized in Russia before large-scale trials.
FDA Commissioner Stephen Hahn told the Financial Times in an interview published on Sunday that his agency was prepared to authorize a coronavirus vaccine before large-scale Phase III clinical trials were complete, as long as officials are convinced that its benefits outweigh the risks.
On Monday, WHO officials said rushing out a vaccine could pose risks.
"If you move too quickly to vaccinate ... millions of people, you may miss certain adverse effects," said Mike Ryan, the head of WHO's emergencies program.
WHO chief scientist Soumya Swaminathan said the FDA's approach was "not something that you do very lightly." She said the WHO's preferred approach would be to have a full set of data that could be used for the pre-qualification of vaccines.
US President Donald Trump has been critical of the WHO's handling of the coronavirus pandemic, accusing it of being too focused on China and issuing bad advice. In May, Trump announced the United States was cutting ties to the organization.
Phase III trials involving tens of thousands of healthy volunteers that test experimental vaccines against a placebo are considered necessary to determine safety and efficacy before they are given to hundreds of millions people to prevent or lessen the severity of Covid-19.