I voted both are associated with terrorism but different.
My rationale was similar to kimmy's in that the act is intended to cause fear.
I would also add a couple of other commonalities. First is the obvious sense of apathy and the second is the element of self-sacrifice for the greater good of a uniform society. One wants everyone to look like them, the other want everyone to think like them, and both are willing to sacrifice themselves and kill in order to get there.
As a quick clarification, I know Islamic terrorism is a complex ideology and I'm not talking about revenge attacks in this comparison; merely attacks in the name of an Islamic caliphate which I see similar to white nationalism.