Most of the time, I wouldn't call a raise with KTs unless I was in the BB or the game has been really loose. There's no way you'd push him off AK, because combined with the chances you're semi-bluffing or raising with a weaker hand than his and the chance he picks up his gutshot straight, he'll call one more bet. (He's calling $60 for about a $600 pot). You know you're way behind on the turn re-raise. He has either AT, KQ, or possibly KJ (although less likely). The river diminishes the chance he has KQ, but it's still a candidate. AT is probably what he has though. Check/fold, unless he's a maniac, then you can call and hope the odds are less than 13-1 that he's bluffing (doubtful otherwise).