I don't want the LOG be writed to /var/log/messages

[openbsd shen <openbsd.shen@xxxxxxxxx>]

I write a line in /etc/syslog.conf:
kern.=info                                              /var/log/iptables

Now the log of iptables write to /var/log/iptables, but I found that
the log still write in /var/log/messages, now I have 2 copies of the
log, how can I stop the write to /var/log/messages, and only write to
/var/log/iptables?
Thanks.