South Korea said Friday that it is investigating two more suspected cases of African swine fever from farms near its border with North Korea, as fears grow over the spread of the illness that has decimated pig herds across Asia.

Quarantine officials wearing protective gear stand as a precaution against African swine fever at a pig farm in Paju, South Korea, Tuesday, Sept. 17, 2019. (Photo: AP)

South Korea's Ministry of Agriculture, Food and Rural Affairs and the Gyeonggi provincial government said officials are testing samples of dead pigs from two farms in Paju, a city where the country's first case of the disease was confirmed Monday. Test results were expected to come out as early as late Friday.

A second case of the disease was confirmed Tuesday in the nearby town of Yeoncheon.

African swine fever is harmless to humans but highly contagious and fatal for pigs as there is no known cure. It has decimated herds in China and other Asian countries.

South Korea has stepped up efforts to contain the disease, which may have crossed from North Korea, where an outbreak was reported near its border with China in late May. South Korean workers had culled some 10,400 pigs at border area farms as of Friday morning.

The ministry said quarantine officials were carrying out blood tests of pigs at some 100 farms within 10 kilometers (6 miles) of the infected farms in Paju and Yeoncheon, and that samples from 56 farms had come back negative.

There are about 6,300 farms in South Korea that raise more than 11 million pigs. South Korean officials have said the next three weeks would be crucial for fighting the outbreak, considering the disease's incubation periods.

Officials have stepped up efforts to disinfect farms and vehicles, while imposing temporary bans on farms near the border from transporting their pigs to other areas.

Park Byeong-hong, an agriculture ministry official, said officials have also started inspections of some 200 slaughter houses, feed factories and artificial insemination facilities that deal with large numbers of pig farms across the country.

More traps and nets will be installed to capture wild boars that roam in and out of North Korea, which some experts see as a potential source of the outbreak in South Korea.

"It's crucial to strictly restrict the movement of people, cars and animals and also prevent (pigs) from contact with wild boars," Park said.

North Korea in recent months has virtually scrapped all diplomatic activity and cooperation with South Korea amid a standstill in nuclear negotiations with the United States, complicating efforts at preventing the North Korean outbreak from spreading to areas near the border.

South Korea's Unification Ministry, which deals with affairs with the North, said Friday that Pyongyang is continuing to ignore Seoul's calls for joint quarantine efforts to fight the disease.