The United States has bought up virtually the whole supply of a drug that could shorten the recovery time of coronavirus patients.
Remdesivir, an antiviral drug, is made by biopharmaceutical company Gilead Sciences.
America has secured more than 500,000 treatment courses through September.
That represents 100 per cent of Gilead’s projected production for July, and 90 per cent for each of the next two months.
But the US has been accused of "undermining" the global effort to fight the coronavirus pandemic.
Business minister Nadhim Zahawi said in buying all supplies of remdesivir the US was not helping the global effort, saying the UK was working "responsibility so we actually deal with pandemic in a way that helps all of the world."
He added: "By attempting to compete we ultimately undermine all our strategies."
Oxford University's Professor Peter Horby, who chairs the new and emerging respiratory virus threats advisory group (Nervtag) said manufacturer Gilead would be under "certain political pressures locally" as a US company.
Alex Azar, the US health secretary, said: "President Trump has struck an amazing deal to ensure Americans have access to the first authorised therapeutic for Covid-19. To the extent possible, we want to ensure that any American patient who needs remdesivir can get it.
"The Trump Administration is doing everything in our power to learn more about life-saving therapeutics for Covid-19 and secure access to these options for the American people.”
Gilead has priced remdesivir at $2,340 per patient for wealthier nations.
The price tag is slightly below the range of $2,520 to $2,800 suggested last week by US drug pricing research group the Institute for Clinical and Economic Review (ICER).
Remdesivir is expected to be in high demand as one of the only treatments so far shown to alter the course of the virus.
After the intravenously administered medicine helped shorten hospital recovery times in a clinical trial, it won emergency use authorisation in the United States and full approval in Japan.
The company is developing an inhaled version that could be used outside a hospital setting.
Remdesivir had previously failed as an Ebola treatment and has not shown that it can reduce coronavirus deaths.