President Park had been due in the United States to meet President Barack Obama on Tuesday. Her office said the coming week would be a "watershed" for the country's response to the respiratory disease for which there is no cure or vaccine.

"President Park decided to postpone the US trip in order to help end the outbreak of MERS and take care of public safety," according to her senior press secretary, Kim Sung-Woo.

A total of 3,439 people in South Korea are in quarantine after coming into contact with MERS patients. There are 108 patients confirmed with MERS. Quarantine has been lifted for 641 people, the ministry said.

In response to the outbreak, 22 universities and more than 2,400 schools, mostly in Seoul and the surrounding Gyeonggi province, have been closed. Many people on the streets are wearing face masks, while attendance at public events, movie theaters and baseball games has fallen dramatically.

MERS was first identified in humans in 2012. It is caused by a coronavirus from the same family as the one that triggered China's deadly outbreak of Severe Acute Respiratory Syndrome (SARS) in 2003.

The 75-year-old woman and 62-year-old man who died were both cancer patients. They contracted the virus at Samsung Medical Center, a major hospital in southern Seoul which has seen the greatest number of total infections and where 10 of the 13 new patients were also infected. Two of the others are being treated in the central city of Daejeon and one near a southern suburb of Seoul.

All nine people who have died in South Korea so far had been suffering serious ailments before they tested positive for the MERS virus, according to the Health Ministry.

The MERS cases in South Korea have all been traced to a man who developed the disease after returning from a trip to the Middle East in early May. He then came into contact with other patients at a hospital before being diagnosed. The first infected patient was diagnosed on May 20.

The new cases bring the total number of MERS patients globally to 1,257, with at least 448 related deaths. South Korea has the second highest number of cases after Saudi Arabia, according to the European Centre for Disease Prevention and Control.

According to World Health Organization data, MERS has a fatality rate of around 35 percent.

jm/sms (Reuters, AFP)