Authorities were on alert as South Korea identified three new cases of a more contagious COVID-19 variant from the UK on Thursday.

The Korea Disease Control and Prevention Agency said in a press briefing Thursday that three individuals had been confirmed infected with the variant first identified in the UK.

The three belong to the same family as another patient, who was found to have the UK variant earlier after arriving in Korea from Britain in mid-December. With the addition of the three new cases, the KDCA said Korea had confirmed 15 cases of the newer strain as of Thursday afternoon.

In response, on Friday the country will start mandating negative COVID-19 test results for foreigners arriving in Korea. The tests must be taken within 72 hours of departure.

Arriving passengers will also be required to undergo additional testing throughout their two-week mandatory self-quarantine. The country earlier announced that it would extend its suspension of direct flights from Britain for two more weeks until Jan. 21, having started Dec. 23.

Initial analyses found that the new variant could be up to 70 percent more transmissible than the original strain. The KDCA plans to conduct more tests on those who have traveled here from Britain and South Africa to uncover any hidden cases.

The alarming news comes as Korea was growing optimistic after reporting fewer than 1,000 cases per day for three consecutive days.

Korea on Thursday announced 870 new COVID-19 cases reported the previous day -- 833 locally transmitted and 37 imported from overseas -- raising the total number of cases recorded in Korea to 66,686. The country added 840 new cases Wednesday and 715 on Tuesday.

By Wednesday’s end, Korea had also reported a total of 1,046 deaths from the coronavirus, up 19 from a day earlier. The number of COVID-19 patients in serious or critical condition reached 400, down from 411 people a day earlier.

Mass infection clusters continued to be traced to eldercare facilities, and a detention center in Seoul was the second-largest source of infections in Korea, with more than 1,000 cases since the first was discovered in late November.

Health authorities vowed to run more COVID-19 checks and heighten monitoring at long-term care facilities and correctional centers to prevent mass infections and identify hidden cases.

At the moment, the government is imposing Level 2.5 social distancing rules in Seoul, Incheon and Gyeonggi Province and Level 2 rules for the rest of the country until Jan. 17. An additional ban on private gatherings of five or more people is to expire on the same date.

Level 2.5 rules categorically disallow the operation of indoor sports facilities, but the government last week made exceptions allowing small cram schools and ballet and taekwondo schools in the capital region to hold classes for up to nine children at a time.

Complaints immediately followed from small merchants and gym operators, who said they too should have been allowed to operate. Owners of coffee shops, bars and internet cafes joined the movement, asking the government to revise the guidelines and compensate them for their losses.

Faced with growing criticism, the government said Thursday that indoor sports facilities would be allowed to operate starting Friday, with the same cap of nine children at a time.

The Greater Seoul area will also allow high-risk entertainment businesses like bars, clubs and karaoke places to reopen Jan. 17, when the current social distancing rules expire.

Prime Minister Chung Sye-kyun said in a meeting Thursday that the government would take steps to ensure fairness and address the financial difficulties facing small businesses, with details to be announced in the coming days.

“As frustration continues and seems endless, people have questioned the virus control standards and there were movements from some sectors opposing them in groups,” Chung said.

“The threat from this third virus wave is getting longer from the seasonal effect and cumulated social fatigue. The government will do better.”

With the COVID-19 pandemic wreaking havoc on the population, government officials and lawmakers have started reviewing whether to provide emergency relief funds for the fourth time since the outbreak started in January last year.

Korea has so far prepared three rounds of emergency relief payments to help people weather the pandemic. The latest is to be distributed starting Monday to small merchants whose profits were affected by the government restrictions.

According to a Realmeter poll of 500 adults released Wednesday, 68.1 percent of respondents were in favor of a fourth round of emergency relief and 30 percent opposed the idea.

Backed by favorable public opinion, the ruling Democratic Party is pushing to extend emergency funding to all people before the Seoul mayoral by-election in April.

“It is more likely that the handout is for the general population as a means to boost the economy,” Rep. Kim Jong-min of the ruling party said in an MBC radio interview on Thursday.

“A treatment is expected to come out in January, and the number of daily new cases could fall below 500 from the effects of social distancing rules. All these factors are considered in coming up with the plan.”

By Ko Jun-tae (ko.juntae@heraldcorp.com)