How To Get The Id Of Updatepanel Which Initiated A Postback

I need to intercept server callback after udate panel async post back and determine which panel initiated the request. The code is pretty simple:

Sys.WebForms.PageRequestManager.getInstance().add_pageLoaded(InterceptUpdateCallback);
function InterceptUpdateCallback(sender, args)
{
var updatedPanels = args.get_panelsUpdated();
for (idx = 0; idx < updatedPanels.length; idx++) {
if (updatedPanels[idx].id == "myUpdatePanel") {
StartSmth();
break;
}
}
}

And it works when UpdatePanel is not inside another UpdatePanel. But when it is inside another UpdatePanel updatedPanels[idx].id has parent Updatepanel id. So how can I get the id of UpdatePanel which initiated the request (the inner UpdatePanel)?