An official investigating the case of Indian doctor Mohammed Haneef "dropped dead" at work amid enormous pressure, Australian Federal Police Commissioner Mick Keelty said on Thursday.

Keelty said the man died of natural causes last week amid intense pressure on the AFP.

"There are enormous pressures here. One thing that I haven't spoken about publicly is that one of the investigators dropped dead in the investigation room on Monday last week. The investigation team has been through a very emotional and stressful time," he was quoted as saying in the media on Thursday.

Haneef is being held in detention on charges of recklessly supporting a terrorist group.