Officials on the US West Coast have reported three unexplained coronavirus cases, raising concerns the virus could be spreading within the community, the BBC has reported.
According to BBC report, the patients - in California, Oregon and Washington State - have no known connection to a badly hit country.
A total of 59 coronavirus cases have been confirmed in the US, according to the World Health Organization (WHO). South Korea, which has the highest number of cases outside China, mobilised the army on Saturday. Soldiers are disinfecting large parts of Daegu, the south-eastern city that has been at the centre of the country's coronavirus outbreak.
On Friday health officials in California's Santa Clara County said an older woman with chronic health conditions had been diagnosed with Covid-19.
Officials say she is not known to have travelled to a country badly affected by the virus or been in contact with a person who had. "This new case indicates that there is evidence of community transmission but the extent is still not clear," said Dr Sara Cody, director of the Santa Clara County Public Health Department.
Oregon health officials said a school employee in Clackamas County had tested positive for the virus. In Washington State, authorities said another case concerned a high school student in Snohomish County. Neither had any contact with a known case nor any history of travel to an affected region. These bring the total of unexplained cases in the country to four, after another such case was reported in California on Tuesday.
The Democratic Party has criticised President Donald Trump's response to the outbreak, arguing that he has contradicted his own health officials and tried to downplay the severity of the virus.
On Friday, the president hit back at Democrats, accusing them of politicising the outbreak. "This is their new hoax," he told a rally in South Carolina. He accused Democrats of advocating a policy of open borders and said this was "a direct threat to the health and wellbeing of all Americans".
However, these are not the first untraced cases. Earlier this week a patient who had no known connection with an affected region died in France.
On Friday, a patient diagnosed with the virus in England was said to be the first to catch it in the UK. The latest developments came as the WHO on Friday upgraded the global risk of the outbreak to its highest level.
But the UN body said there was still a chance of containing the virus if its chain of transmission was broken. WHO head Dr Tedros Adhanom Ghebreyesus also stressed that fear and misinformation were the biggest challenges to overcome. "Our greatest enemy right now is not the #coronavirus itself. It's fear, rumours and stigma. And our greatest assets are facts, reason and solidarity," he wrote on Twitter.