  Positive frequency Wightman function and vacuum expectation value of the
energy-momentum tensor are computed for a massive scalar field with general
curvature coupling parameter subject to Robin boundary conditions on two
parallel plates located on $D+1$ - dimensional AdS background. The general case
of different Robin coefficients on separate plates is considered. The mode
summation method is used with a combination of a variant of the generalized
Abel-Plana formula for the series over zeros of combinations of cylinder
functions. This allows us to extract manifestly the parts due to the AdS
spacetime without boundaries and boundary induced parts. The asymptotic
behavior of the vacuum densities near the plates and at large distances is
investigated. The vacuum forces acting on the boundaries are presented as a sum
of the self-action and interaction forces. The first one contains well-known
surface divergences and needs further regularization. The interaction forces
between the plates are attractive for Dirichlet scalar. We show that threre is
a region in the space of parameters defining the boundary conditions in which
the interaction forces are repulsive for small distances and attractive for
large distances. An application to the Randall-Sundrum braneworld with
arbitrary mass terms on the branes is discussed.
