unknown directive "thread_pool"

[Richard Kearsley]

Hi
First time trying aio threads on linux, and I am getting this error

[emerg] 19909#0: unknown directive "thread_pool" in 
/usr/local/nginx/conf/nginx.conf:7

Line7 reads:
thread_pool testpool threads=64 max_queue=65536;

Everything indicates it was built --with-threads, so I'm not sure where 
to go from here

nginx -V:
/usr/local/nginx/sbin/nginx -V
nginx version: nginx/1.9.1 built by gcc 4.8.2 (Ubuntu 4.8.2-19ubuntu1) 
configure arguments: --with-debug --with-file-aio --with-threads

from configure output:
Configuration summary
+ using threads

Any help appreciated
Thanks
Richard