"We are as shocked, heartbroken and sad as you are", writes A-Teens to their fans on Instagram.
According to the organizer of the festival Fiesta Grado 3, the reason is the heat wave that has swept over the country, writes Aftonbladet.
Marie Serneholt, Sara Lumholdt, Dhani Lennevald and Amit Paul reunited last year when they performed at Melodifestivalen.
The band's performance on Sunday still seems to be on as the event is moving to the city of Concepción.
"We hope to meet as many of you as possible tomorrow", writes A-Teens.
