Friendly URL without www and with 301 redirect

I'm using the following code in my .htaccess to make a system of URLs friendly to a PHP site.

<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteRule ^(.*)$ index.php?url=$1
</IfModule>

I would like to make a permanent redirection of all URLs that start with www to URLs without www but maintaining the same system of friendly addresses. Does anyone have any idea how I could resolve this?