The United States expressed deep concern about North Korea’s vulnerability to the outbreak of a new virus and said it was ready to support efforts by aid organizations to contain the spread of the illness in the impoverished nation. North Korea has moved to strengthen quarantines and other preventive measures to protect itself from the COVID-19 illness that has killed hundreds and sickened tens of thousands in China, North Korea’s neighbor and closest ally. North Korea has yet to report a case of the new virus, but state media have hinted that an uncertain number of people have been quarantined after showing symptoms.