Dozens of US Secret Service personnel have been told to self-isolate after two who attended President Donald Trump's rally in Tulsa on Sunday tested positive for Covid-19, US media report.
Mr Trump was criticised for holding the re-election campaign event in a city where the infection rate is rising.
Six members of the campaign's advance team tested positive before the rally, while two others did so afterwards.
The Secret Service did not say how many employees were infected or isolating.
The Washington Post reported that the the six advance team members who tested positive before Saturday's rally included two Secret Service personnel.
They both attended a planning meeting on Friday along with dozens of other Secret Service agents and officers, who continued to carry out their duties after the test results were known, the newspaper cited people familiar with the situation as saying.
A law enforcement official told CNN that the number of agents in quarantine was in the "low" number of dozens.
Secret Service spokeswoman Catherine Milhoan said the agency remained "prepared and staffed to fulfil all of the various duties as required".
"Any implication that the agency is in some way unprepared or incapable of executing our mission would be inaccurate," she added.
CNN also cited an internal email as saying that Secret Service agents involved in presidential trips must now be tested 24 to 48 hours before deployment.
People who attended the rally in Tulsa were not required to wear face masks or follow social-distancing guidelines, but they did have to pass temperature checks.
They also had to sign a waiver protecting the Trump campaign from responsibility for any illness.
According to Tulsa's fire department, about 6,200 people attended the event - a third of the capacity of the venue. But that was denied by the Trump campaign, which said twice as many people were inside.
It is not yet known if the rally will have an impact on infection rates in Tulsa. But on Wednesday officials reported a record 259 new confirmed cases in the city.
Meanwhile, New York, New Jersey and Connecticut have asked people travelling from states where cases are rising to go into self-isolation for 14 days.
The states affected are Alabama, Arkansas, Arizona, Florida, North Carolina, South Carolina, Texas and Utah, New York Governor Andrew Cuomo told reporters.
The University of Washington predicts 180,000 US deaths by October - or 146,000 if 95% of Americans wear masks.
So far, the US has recorded more than 2.3 million cases of the virus and more than 121,000 deaths. Health officials say the coming weeks will be crucial to stem the outbreaks.