Query with time zone offset but without seconds

I have a column »timestamp with time zone«. I want to extract the date/time in
a different format including the time zone offset in a query but without
seconds. If I do

select to_char(datetime, 'YYYY-MM-DD HH24:MI') from table;

then the time zone offset is missing in the output: 2011-03-25 18:01
If I do

select date_trunc( 'minute', datetime) from table;

then the time zone offset is present, but the seconds are not removed:
2011-03-25 18:01:00+01

I want it to look like this: 2011-03-25 18:01+01

How to do that?

Marco