The Ministry for Food, Agriculture, Forestry and Fisheries said three cattle farms in the eastern province of Gangwon and a pig farm in North Gyeongsang Province tested positive for the disease.
The cattle farms were located in Chuncheon and Hongcheon, about 80-100 kilometers northeast of Seoul, and in Hoengseong, 140km east of the capital city.
The pig farm in Yeongju, with 13,000 animals, is around 230km southeast of Seoul and relatively close to where the first outbreaks were reported last month.
All four farms had been quarantined as of Monday after some animals started to drool excessively, refused to eat and developed blisters on their snouts, tongues and hooves.
The 13,147 pigs and cows on the farms have been ordered destroyed to prevent further spread of the disease, with other livestock within 3km of the Incheon farm and 500 meters of the two cattle farms to be culled and buried.
A quarantine official vaccinates cattle at a farm in Yangpyeong, 55 kilometers east of Seoul. (Yonhap)
The ministry also said a cattle farm in Chungju, North Chungcheong Province, in the country's interior, which had previously been FMD-free, reported the existence of the virus among animals that were destroyed as a precautionary move. Because the cattle were culled before tests were conducted, the case is not tallied as an outbreak although a separate quarantine ring will be set up round the farm.
Related to the latest outbreak, the most severe in South Korea's history, the government announced last Wednesday that it will opt to vaccinate cattle after nationwide quarantine and decontamination efforts failed to prevent the disease from spreading.
It said over the weekend that vaccinations will be expanded to counter new outbreaks in the southeastern parts of Gyeonggi Province. More than 184,057 animals on 7,500 farms and ranches are earmarked for vaccination although the numbers may be adjusted.
"Authorities are closely monitoring the spread of the disease and, if need arises, may order more animals to be vaccinated," a ministry official said.
After the first case was confirmed on Nov. 29 in North Gyeongsang Province, the disease spread to Gyeonggi and Gangwon provinces and the city of Incheon, with a total of 60 cases confirmed and more than 471,000 animals ordered destroyed. Counting cases involving animals culled before they were tested, the total number of outbreaks reached 65 cases and includes the Chungcheong region.
Seoul has so far mobilized 155,974 quarantine personnel to man 1,226 checkpoints across the country and to take part in the decontamination and culling process.
FMD is highly contagious and affects all cloven-hoofed animals, such as cattle, pigs, deer, goats and buffalo, although it is harmless to humans. It is classified as a "List A" disease by the Paris-based World Organization for Animal Health, with countries that report outbreaks barred from exporting meat.
The country was hit by the disease in 2000 and 2002 and two more times earlier in the year. Authorities have ordered the culling of a record 299,700 livestock so far with losses estimated at 400 billion won (US$347 million).