union and LIMIT problem

Does anybody know how to use UNION and LIMIT together ?
I want to get 10 rows from publications and 10 rows
from keys.

select msg_id from publications limit 10 union
select key_id from keys limit 10
produces
ERROR: parser: parse error at or near "union

select msg_id from publications union
select key_id from keys limit 10
produces something I wasn't expected

Regards,

Oleg

_____________________________________________________________
Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
Sternberg Astronomical Institute, Moscow University (Russia)
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(095)939-16-83, +007(095)939-23-83