  In this paper, we formulate a new local move on virtual knot diagram, called
arc shift move. Further, we extend it to another local move called region arc
shift defined on a region of a virtual knot diagram. We establish that these
arc shift and region arc shift moves are unknotting operations by showing that
any virtual knot diagram can be turned into trivial knot using arc shift
(region arc shift) moves. Based upon the arc shift move and region arc shift
move, we define two virtual knot invariants, arc shift number and region arc
shift number respectively.
