How to interpolate a points raster file (gridded)?

Dear All,

I have a points raster file (e.g. crop yield derived from RS) and I want
to interpolate these discrete points in this 2D raster domain into a
continuous crop yield surface for other further use. I knew I can do it
in ILWIS and GRASS, but not sure within R.
Any comments are appreciated.

Regards

Yong Li