The US and South Korean militaries on Thursday postponed forthcoming joint exercises due to the coronavirus outbreak as the Asian country reported 334 new cases, taking its total to 1,595.
The decision to delay the training was made after Seoul declared its highest "severe" alert level over the virus, Combined Forces Command said, adding the postponement was "until further notice".
The United States has 28,500 troops in South Korea to protect it against the nuclear-armed North, many of them based south of Seoul at Camp Humphreys in Pyeongtaek -- Washington's biggest overseas military facility.
The security allies have previously scaled back their annual joint military exercises significantly to facilitate nuclear talks with Pyongyang -- which condemns such drills as preparations for an invasion -- but a command coordination exercise had been planned for this spring.
South Korea has the highest number of virus cases in the world outside China, where the disease first emerged in December and has since spread to dozens of countries.
Thursday's increase was the biggest reported so far by the Korea Centers for Disease Control and Prevention, which gave a death toll of 12.
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More than 80 percent of the South's cases are in Daegu -- South Korea's fourth largest city with a population of 2.5 million -- and the neighbouring province of North Gyeongsang.
They centre on the Shincheonji Church of Jesus, a secretive entity often accused of being a cult.
A 61-year-old female member developed a fever on February 10, but attended at least four church services in Daegu before being diagnosed.
Checks have begun on more than 200,000 Shincheonji members after the organisation handed over a list to authorities, and the number of cases is expected to increase as a result.
South Korea has an advanced medical system, a free press and a strong culture of public accountability, and observers say that its health statistics can be treated with confidence.
Officials have urged the public to exercise extra caution, advising citizens to stay home if they have a fever or respiratory symptoms.
An American soldier stationed at Camp Carroll 30 kilometres (19 miles) north of Daegu was put in self-quarantine at his home Wednesday after testing positive for the virus, the first case among US Forces Korea personnel.
Scores of events have been cancelled or postponed as the outbreak has spread in the world's 12th-largest economy, from K-pop concerts to the start of the K-league football season, while museums and other public venues have closed.
The Bank of Korea on Thursday lowered the country's growth outlook for this year to 2.1 per cent, down 0.2 percentage points, citing a contraction in consumption and slowing exports due to the spread of the virus.
The Catholic Church in South Korea said it would suspend all public masses at more than 1,700 churches across the country in response to the contagion.
A group of Catholics who recently returned from a pilgrimage to Israel had been one of the cluster infections.