The World Health Organization says it has been informed of four additional infections with the new coronavirus, including two people in one family in Saudi Arabia.
The WHO says two other members of the same family were sick with similar symptoms.
The UN agency's statement does not address the question of whether the family members may have been infected by an animal or environmental source, or whether the virus may have spread from person to person.
Of those four sick family members, two have died; one tested positive for the virus and testing is still underway on samples from the other.
Of the two members of the family who were sick but survived, one tested negative for the new coronavirus.
Three of the new four cases were reported from Saudi Arabia and the fourth from Qatar.
That brings to six the total of confirmed cases of infections with the new virus, which is in the same family of viruses as SARS.
The new virus was spotted for the first time in June, when a man from Saudi Arabia died after a serious respiratory infection. But word of the discovery of the new virus did not emerge until late September.
To date Saudi Arabia and Qatar have been the only two countries to report cases, with four in the former and two from the latter. Of the six cases, two have died.
But the WHO says other countries should be on the lookout for similar cases.
"Until more information is available, it is prudent to consider that the virus is likely more widely distributed than just the two countries which have identified cases," the agency's statement says.
"Member states should consider testing of patients with unexplained pneumonias for the new coronavirus even in the absence of travel or other associations with the two affected countries."
It also suggests countries should investigate any clusters of severe acute respiratory infections, in the community or among health-care workers. Health-care workers can serve as sentinel in disease outbreaks because they can become infected by unidentified cases.
There is little information about the new cases. The WHO statement does not identify whether the cases are men or women, nor does it give their ages or whether they lived in cities or the countryside.
Nor does the statement hypothesize how any of the people may have become infected.
International teams of researchers have travelled to Saudi Arabia to investigate possible sources of the new virus. To date they have not publicly revealed whether they found any clues to its source.
The genetic blueprints of virus samples from the first two cases suggest the viruses come from bats. But it is not known at this point whether the viruses jumped directly from bats to people — say through exposure to bat guano or urine — or from bats to other animals and then to humans.