South Korea's new virus cases stayed below 40 for the second day in a row on Wednesday, but imported cases continued to rise, hampering the country's efforts to contain the virus.

The country added 39 cases, including 11 local infections, raising the total caseload to 13,551, according to the Korea Centers for Disease Control and Prevention (KCDC).

Infections coming in from overseas have been on a high plateau for weeks, with double-digit numbers of new cases for 20 consecutive days.

Of 28 additional imported cases reported, 23 were detected at quarantine checkpoints of airports and sea ports. The country reported 43 imported cases Monday, a four-month high.

Since Monday, the country has required arrivals from four high-risk nations -- Bangladesh, Pakistan, Kazakhstan and Kyrgyzstan -- to submit a certificate showing they tested negative for the virus.

The government said two more countries will be added to the list Monday, without disclosing the names for diplomatic reasons.

Imported cases, once the main source of virus cases here, fell to a single-digit figure early last month on the back of the country's strengthened quarantine checks at airports.

But such cases have bounced back to double-digit numbers since mid-June as global virus cases have bounced back amid eased lockdowns.

Also, the number of foreign workers entering the country for the summer season increased recently.

The number of new local infections stayed between 20 and 40 in July but shrank to 19 on Monday and 14 on Tuesday. The total on Wednesday was the lowest since June 22, the KCDC said.

Since last Friday, the country has banned churches from organizing smaller gatherings other than regular worship services and having group meals. QR code-based entry logs also have been applied to churches.

A total of 126,000 facilities across the country have adopted the QR code-based system.

Sporadic cluster infections across the country also continued to weigh on the country's efforts to contain the spread of COVID-19, with most tied to religious facilities and door-to-door retailers.

"We sincerely ask middle-aged and senior people to refrain from participating in door-to-door retailers' events or other kinds of PR events," KCDC Deputy Director Kwon Joon-wook said in a briefing.

Of 141 COVID-19 patients tied to a door-to-door retailing event in Gwangju, 101, or 72 percent, are those aged 50 or older, the KCDC.

The densely populated Seoul and adjacent areas accounted for most of the local infections last month, but virus outbreaks have been consistently reported in other parts of the country.

Of local transmissions, six cases were reported in Seoul, three in Gyeonggi Province surrounding the capital city, the KCDC said.

Cases tied to an office building in Seoul's southwestern ward of Gwanak reached nine as of noon, up one case from the previous day. Those linked to a building in the capital's southern district of Gangnam went up by one to nine cases.

The southwestern city of Gwangju reported one more case Wednesday. The city has recently emerged as a new hotbed of the virus outbreak outside of the Seoul metropolitan area.

South Korea reported no additional death, bringing the death toll to 289, the KCDC said. The fatality rate was 2.13 percent.

The total number of people released from quarantine after full recoveries stood at 12,348, up 66 from the previous day.

The country has carried out 1,431,316 tests since Jan. 3. (Yonhap)