South Korean and Chinese officials have been trading barbs for weeks over who’s to blame for a spike in air pollution in Seoul this winter.

South Korean President Moon Jae-in on Jan. 22 said South Koreans suffered last week due “an unprecedented number of days of dense fine dust” and said he was “well aware of the fact that our people have great concerns about fine dust coming from China,” South Korea’s Yonhap News Agency reported.

Moon called for more cooperation with China and the joint establishment of an early...