Temperatures have hit 34 degrees Celsius in Saemangeum, near the city of Buan on South Korea’s west coast, where 39,000 participants, mostly scouts aged 14 to 18, are camping.
The pullout by the United States comes as a further blow to the organisers and the South Korean government, which on Friday had said it would send more water trucks, air-conditioned spaces and medics to save the event.
Scouts from Britain, the largest grouping at the jamboree, said on Friday they were moving to hotels in Seoul for the rest of their stay, to alleviate pressure on the site.
The World Organization of the Scout Movement also said in a statement on Friday that it had asked the Korean Scout Association to consider “alternative options to end the event earlier than scheduled and support the participants until they depart for their home countries”.