  In order to constrain the properties of dense and warm gas around active
galactic nuclei, we have searched Infrared Space Observatory spectra of local
active galactic nuclei for the signature of the 4.7micron fundamental
ro-vibrational band of carbon monoxide. Low resolution spectra of 31 AGN put
upper limits on the presence of wide absorption bands corresponding to
absorption by large columns of warm and dense gas against the nuclear dust
continuum. High resolution (R~2500) spectra of NGC 1068 detect no significant
absorption or emission in individual lines, to a 3sigma limit of 7% of the
continuum. The limits set on CO absorption in local AGN are much lower than the
recent Spitzer Space Telescope detection of strong CO absorption by dense and
warm gas in the obscured ultraluminous infrared galaxy IRAS F00183-7111,
despite evidence for dense material on parsec scales near an AGN in both types
of objects. This suggests that such deep absorptions are not intimately related
to the obscuring `torus' material invoked in local AGN, but rather are a
signature of the peculiar conditions in the circumnuclear region of highly
obscured infrared galaxies like IRAS F00183-7111. They may reflect fully
covered rather than torus geometries.
