Nginx redirection cycle with X-Accel-Redirect

Trying to get nginx to work with the X-Accel-Redirect header. I'm getting this error:

*24 rewrite or internal redirection cycle while internally redirecting to "/app/index.php", client: 127.0.0.1, server: project.dev, request: "GET / HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "project.dev"

nginx site conf:

server {
    listen      80;
    server_name project.dev;
    root        /www/project;

    location ^~ /f/ {
        internal;
        alias /www/project/files/;
    }

    location / {
        try_files $uri /app/index.php$is_args$args;
    }

    include php.conf;
    include apache.conf;
}

/www/project/app/index.php

<?php
header('X-Accel-Redirect: /f/image.jpg');
exit;

I added ^~ to the location block, because I thought that would terminate the matching of location blocks, and therefor solve this. This might be a misunderstanding from my part.

Any idea how to fix this?

Update with php.conf and apache.conf

php.conf:

# pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
#
location ~ \.php$ {
  fastcgi_pass   127.0.0.1:9000;
  fastcgi_index  index.php;
  fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
  include        fastcgi_params;
}

apache.conf:

# deny access to .htaccess files, if Apache's document root
# concurs with nginx's one
#
location ~ /\.ht {
    deny  all;
}