I was wondering what are the key differences between kenjutsu and kendo?
I know that kendo is considered as an art of fighting where as the kenjutsu is the art of killing, or am I wrong here?
Kenjutsu is the skill of using the sword, divided into various styles by ryuha (roughly, "schools"). This can include skills such as drawing (iai) or engaging (battou), as well the disarming of an armed opponent (shinken shirahadome or muto dori). Generally (though certainly not in all cases), kenjutsu is one component of a greater curriculum within a ryuha and is taught as a means to kill an opponent.
Kendo is a martial art with sport-like elements of competition. It originated in the 18th c. with the development of shinai and bogu as training tools for students of kenjutsu, and was changed heavily by the banning of militaristic activities following WWII when, in 1950, it was reintroduced into public life as "Shinai Competition" (shinai kyougi), then in 1952 was again renamed to kendo under the governance of the "All Japan Kendo Federation" (Zen Nihon Kendo Renmei or ZNKR). Modern kendo is much heavier in competition, whereas the origins of the art were a means of practicing the skills of kenjutsu in a safe manner (using shinai [bamboo sword] and bogu [armor]).
Kendo has much stronger philosophical ties to Buddhism than kenjutsu on its own. While specific ryuha teaching kenjutsu may have religious or philosophical views, concepts of mushin, fudoshin, and zanshin (all related to the doctrine of Fudo Myo-o) are essential to the practice of Kendo.
Your question may be answered more generically as thus:
What is the difference between -do and -jutsu? (with the exception of judo and jujutsu)
-Jutsu, grossly, means 'technique'. It means something applicable, practical, extremely concerned with getting results.
-Do, grossly, means 'path'. It has much stronger ties to a lot of other aspects of life, including but not limited to social and spiritual.
As a summary, you may find interesting to note that budo and bujutsu, on wikipedia, refer to the same article - Budo. Here is the key point from this article, related to the difference:
Budo and bujutsu have quite a delicate difference; whereas bujutsu only gives attention to the physical part of fighting (how to best defeat an enemy), budo also gives attention to the mind and how one should develop oneself.
Any further talk would just be expanding on this sentence.