Lock users out of Active Directory with ASP.NET application - asp.net

Question

We have an intranet ASP.NET 4.0 application and use forms authentication where employees authenticate against Active Directory to log in.
We need to lock users out of AD after too many failed password attempts (number is set in domain policy).
As it works now, users get locked out of the application only but not out of AD. We need to lock them in AD and they will need to call help desk to unlock them.
I saw this http://msdn.microsoft.com/en-us/library/ms998360.aspx, where it is stated under "Account Lockout" that ActiveDirectoryMembershipProvider locks users out of provider but not out of AD.
But how do we lock users in AD then?
web.config:
<membership defaultProvider="MyADMembershipProvider">
<providers>
<add name="MyADMembershipProvider"
type="System.Web.Security.ActiveDirectoryMembershipProvider, System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"
connectionStringName="ADConnectionString"
connectionUsername="administrator"
connectionPassword="passw0rd"
attributeMapUsername="sAMAccountName" />
</providers>
</membership>
Login.aspx:
<asp:Login ID="Login1" runat="server" DisplayRememberMe="False" FailureText="Wrong user name or password." DestinationPageUrl="~/User.aspx" OnLoggedIn="Login1_LoggedIn" OnLoginError="Login1_LoginError">
Login.aspx.cs
protected void Login1_LoginError(object sender, EventArgs e)
{
string userName = Login1.UserName;
if (!string.IsNullOrEmpty(userName))
{
// Get information about this user
MembershipUser usr = Membership.GetUser(userName);
if (usr != null)
{
// check to see if the error occurred because they are not approved
if (!usr.IsApproved)
{
Login1.FailureText = "Your account has not yet been approved by an administrator.";
}
// check to see if user is currently locked out
else if (usr.IsLockedOut)
{
Login1.FailureText = "You have been locked out of your account due to too many failed passwords. Call help desk to unlock it.";
}
}
}
}