The virus has infected 138 people in South Korea and killed 14.
The World Health Organization (WHO) said on Saturday it would hold an emergency meeting on Tuesday to consider South Korea's outbreak of Middle East Respiratory Syndrome (MERS), which it described as "large and complex".
The UN health agency said more cases should be anticipated, but that the disease was confined to hospitals, with no sign it was spreading in the community.
There was also no indication that the MERS virus in South Korea had changed to become more transmissible, the WHO's assistant director general, Keiji Fukuda, told a news conference at the Health Ministry in Sejong, south of the capital, Seoul.
The virus has infected 138 people in South Korea and killed 14 of them since it was first diagnosed on May 20 in a businessman who had returned from a trip to the Middle East.
The 12 new cases reported on Saturday included an ambulance driver who transported an infected person.
The meeting on Tuesday of the MERS emergency committee, which comprises international health experts from WHO member states, will provide technical updates on epidemiology and provide advice on future actions to be taken in r
© Thomson Reuters 2015