Symfony2 app in subdirectory of nginx configuration

Symfony2 app in subdirectory of nginx configuration

I'm trying to set up my environment such that surveyadmin.local points at
one directory and surveyadmin.local/api points at another.
However, no matter what I change, the /api URL always results in a call to
the directory that surveyadmin.local is pointing at.
Here's my config for the vhost in question:
server {
listen 80;
server_name surveyadmin.local;
location / {
root /srv/http/surveytool/admin/build;
index index.html;
}
location /api {
root /srv/http/surveytool/api/SurveyTool/web;
index app.php;
try_files $uri $uri/ /app.php?$query_String;
location ~ \.php(?|$) {
fastcgi_pass unix:/var/run/php5-fpm.sock;
fastcgi_index app.php;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include /etc/nginx/fastcgi_params;
}
}
access_log /var/log/nginx/surveyadmin.access.log;
error_log /var/log/nginx/surveyadmin.error.log debug;
}
What am I doing wrong? How do I force nginx to do what I want?