South Korea reported three new cases of Middle East Respiratory Syndrome, or MERS, on Sunday.
A doctor and another health care worker were among the new cases, according to the French news agency.
The disclosure of the new cases follows the announcement that no new cases reported Saturday, which raised hopes the country was winning the battle against the deadly virus.
The Health Ministry has also reported the death of a MERS patient, raising the death toll from the virus to 25.
Nearly 170 people have been sickened by the virus, which cannot be controlled by any known vaccine.
Elsewhere in the region, Thai Prime Minister Prayuth Chan-ocha has urged people not to panic after the country's first confirmed case of MERS was reported this past week.
Officials say Thailand is well prepared to deal with public health issues arising from a MERS outbreak. Already, 59 people who may have been exposed to the virus are being monitored, either in hospitals or at their homes.
The World Health Organization has blamed the extent of the outbreak in South Korea on the failure of authorities there to implement adequate control measures.
WHO said there was a lack of awareness about the risks of MERS among healthcare workers, and that hospitals' infection prevention and control measures were inadequate. However, the U.N. agency says the outbreak is not yet considered a public health emergency of international concern.
MERS symptoms include fever, coughing and shortness of breath - all of which are typically associated with non-serious illnesses such as the common cold.
Some material for this report came from AP, AFP and Reuters.