delete directory

[Aiza]

This directory named empty has read/exec permissions.
How do I delete it?

# /usr/jails/newjail/var >ls -l
total 2
dr-xr-xr-x  2 root  wheel  512 Nov 21 22:53 empty
# /usr/jails/newjail/var >cd empty
# /usr/jails/newjail/var/empty >ls -l
total 0
# /usr/jails/newjail/var/empty >cd ..
# /usr/jails/newjail/var >rmdir empty
rmdir: empty: Operation not permitted
# /usr/jails/newjail/var >rm -rf empty
rm: empty: Operation not permitted
# /usr/jails/newjail/var >chmod 777 empty
chmod: empty: Operation not permitted