SEOUL - South Korea reported 505 additional coronavirus infections in its largest daily increase on Thursday, as the United States issued a new warning against travel to the Asian nation, and their militaries postponed a joint drill.The new cases take total infections to 1,766, the Korea Centers for Disease Control & Prevention (KCDC) said, for the largest daily jump since the first confirmed infection on Jan. 20. South Korea also reported a 13th death. Of the new cases, 422 were in the southeastern city of Daegu, the location of a church at the centre of South Korea's outbreak, the KCDC said in a statement.The US State Department raised its travel advisory level, urging citizens to "reconsider travel" to South Korea.In Seoul, the capital, people waited in long queues at some stores to buy masks, which have been in short supply, despite only a few dozen infections reported in the city.The past week's sudden surge in cases has ignited criticism of the government's handling of the crisis, particularly a decision to limit arrivals from China, rather than imposing a blanket ban.Feelings on the issue run so high that more than 1 million people have signed a petition demanding the impeachment of President Moon Jae-in.The virus that can lead to pneumonia is believed to have originated in the central Chinese city of Wuhan late last year before killing more than 2,700 and infecting about 80,000, the vast majority in China.The US military reported its first virus case on Wednesday, in a 23-year-old soldier based in Camp Carroll, about 20 km (12 miles) from Daegu.About 28,500 US troops are stationed in South Korea, which remains technically at war with North Korea.The South Korean military has also reported at least 21 infections, and has confined most troops to their bases.A "command post training" exercise usually held by the two militaries' Combined Forces Command is to be postponed "until further notice", the combined command said in a statement.The US commander in South Korea agreed to the delay after a request by the chairman of its joint chiefs of staff.On Thursday, media said a Korean Air flight attendant who tested positive for the virus had worked on flights between Seoul and Los Angeles.The attendant had been on a Korean Air KE958 flight from Israel to Incheon on Feb. 15 and 16, the KCDC has said. Passengers included a South Korea tour group among whom 31 virus cases were seen to have originated.The agency has not released details of other routes and flights flown by the employee.Yonhap News Agency and other media said she worked on flights KE017 and KE012 on Feb. 19 and Feb. 20 to and from Los Angeles. About 30 crew on the same flights are in self-quarantine for 14 days, media added.The United States may in future have to curb travel to Italy, South Korea and other countries over the virus, President Donald Trump said on Wednesday, but now was not the right time.South Korea has the most virus cases outside China and Italy and Iran are emerging as new epicentres of the rapidly spreading illness.