Concatenating parameters in struts2 iframe load

Question

using Struts2, I successfully load an external URL inside a jsp page using an iframe like this:

<iframe src="http://www.abcd.com/somedir/index.php">
</iframe>

I’m also able to pass a request parameter in the URL like this:

<iframe src="http://www.abcd.com/somedir/index.php?sid=999">
</iframe>

The problem comes when I try to concatenate that parameter, loading it from the Strus2 stack:

<iframe src="http://www.abcd.com/somedir/index.php?sid=<s:property value="sid" />">
</iframe>

Could some body help me to achieve that?

Thanks