Seoul will summon Japan's ambassador to protest over "irrational" plans to impose coronavirus quarantine on arrivals from South Korea, it said Friday, accusing Tokyo of ulterior motives.
The two countries have close economic ties and are both major US allies, democracies and market economies faced with a rising China and nuclear-armed North Korea.
But their relationship continues to be heavily affected by Japan's colonial rule of the Korean peninsula from 1910 to 1945 -- a dispute that escalated into a trade and security row last year.
Japanese Prime Minister Shinzo Abe on Thursday announced that foreign arrivals who have recently been in China or South Korea would be required to spend 14 days in quarantine.
Seoul's foreign ministry urged Tokyo to reconsider the "irrational and overbearing" measure in a statement, saying it would summon the ambassador to protest.
"We can't help but question whether Japan has other motives than containing the outbreak," it added.
Seoul could take countermeasures, it signalled, saying it was exploring "all possible options" to ensure the safety of South Koreans.
South Korea's total reported infections -- the largest figure outside China, where the virus first emerged -- rose to 6,284 on Friday, the Korea Centers for Disease Control and Prevention said.
It announced seven more deaths, taking the toll to 42.
Japan has reported 360 confirmed cases and six deaths from the illness.
Around 40 countries and regions have imposed entry bans on foreigners who have recently been in the South, while more than 20 require quarantine, as do several parts of China.
Japan's quarantine announcement was already affecting "thousands of South Koreans", said Park Chul-hyun, a media columnist based in Tokyo, who cancelled a three-day trip to Seoul for fear of having to go into quarantine on his return.
"There are thousands of South Koreans arriving in Tokyo on a daily basis and I bet a majority of them have called off their trips," said Park, criticising the measure as a "pure performance" ahead of the Tokyo Olympics.
Over 90 percent of South Korea's cases are in the southern city of Daegu -- with more than 4,600 cases confirmed there -- and the neighbouring North Gyeongsang province.
Most of the country's infections are linked to the Shincheonji Church of Jesus, a religious sect often condemned as a cult.
A 61-year-old female member of the sect in Daegu developed symptoms on February 10 and attended at least four services before being diagnosed.
Scores of events -- from K-pop concerts to sports seasons -- have been cancelled or postponed over the contagion, with school and kindergarten breaks extended by three weeks nationwide.