Red fire ants found in the southern port of Busan are presumed to be identical to a species in the United States, but further inspection is needed to figure out their exact origin, South Korea's quarantine authority said Tuesday.

Twenty-five fire ants were discovered in a storage container at Busan's Gamman port Sept. 28, and a nest capable of accommodating 1,000 was also found, raising alarm that the highly invasive insects were inadvertently brought into the country.

The Ministry of Agriculture, Food and Rural Affairs said it has conducted emergency quarantine measures and stepped up monitoring to prevent further spread, noting it did not find other ants in the 34 ports and two inland container depots examined so far. 

Although the remains of a queen ant was not found, the ministry tentatively concluded that it already died based on the size and scope of the colony discovered in the cracked asphalt.

"Red fire ants are generally found in the United States, but they have since spread to China, Australia and Japan, giving birth to special genetic variations as they evolve in their new environment," Park Bong-gyun, the chief of the Animal and Plant Quarantine Agency, said in a briefing.

"It is premature to say the red fire ants came from the US at this point, as an in-depth epidemiological inspection into their variation is needed to figure out their origin."

Gamman port received containers from six nations between May and September -- China, Japan, Taiwan, the US, Australia and Malaysia -- with 60 percent coming from China, the ministry said.

Quarantine officials will continue to sterilize the area within a 100-meter radius of the container depot until next week and conduct inspections on the pavement and other areas. 

The ministry said it will work with other related organizations to regularly monitor and inspect major ports to prevent the inflow of red fire ants. (Yonhap)