ISO time zone format

Hi there,

I'd like to format a time stamp with time zone as ISO pattern (e.g. 
1999-01-08 04:05:06 -8:00)

I found the patterns for all the timestamp parts, from "Data Type Formatting 
Functions" Postgresql documentation, excepting the numeric ISO time zone.

Please suggest the appropiate pattern for that.

TIA,
Sabin