Some might be from electromagnetic interactions. But in a nuclear reaction the bigger part of the force is due to the nuclear binding force, or the release thereof. The nuclear force is far stronger than electromagnetic forces. The difference is comparable to the difference between 20 pounds of gunpowder or dynamite or gasoline exploding, which is a lot, maybe enough to take out the windows of a pizzaria, and 20 pounds of uranium or plutonium, which would vaporize almost any small town up to 10,000 population.