It would be better to say, "To all who heard the terrible news, I am sorry that the United States Ambassador was assaulted while he was visiting South Korea." It shows sympathy for what happened, but does not make it look like you were at fault in any way.

Umm... it actually sounds like you were assaulted, not the ambassador. It's not easy to switch it just to "formal" - there are several levels to this. Here's a version which might be what you're looking for: "I feel deeply sorry ("really sorry" is something you say to the people you know personally) to hear of the US ambassador's unfortunate incident..." I'm not sure what you mean by the last half. Are you sorry that people are shocked? Or do you share their feelings? The very end would be "upon/after hearing this news." (So we don't use "incident" twice.) By the way, "i just wanna know" sounds VERY childish. Just use normal English.