Kia says not recommended. That said there are some posts on here showing guys in Europe towing close to 2k lbs. Probably safe in the flatlands but that would be a stretch in hilly areas; the engine doesn't have any problem with it, but the suspension and braking wouldn't be so happy.
Kia says that this care is not recommended for towing. Sure, you can do whatever you want, but don't cry when transmission will die.
Or the engine if you have the 1.6L - you didn't specify anything about your Soul.