Some countries that were preparing to let limited international travel resume are already reconsidering, as clusters of cases grow into new outbreaks. Some European nations were warning citizens not to visit Spain after some of its most beloved summer venues turned into coronavirus hot spots facing renewed pandemic lockdowns. The British government suddenly re-imposed over the weekend a mandatory two-week quarantine for anyone entering the U.K. from Spain. New Zealand officials said their South Korean counterparts suspect the traveler was infected while transiting through Singapore. The number of worst-affected countries where newly confirmed cases are rising still outnumbers countries finally seeing a downward trend in infections, according to data compiled by Johns Hopkins University.