Android: disable DialogFragment OK/Cancel buttons

How can I disable OK/Cancel button of a DialogFragment when it is created using an AlertDialog ? I tried calling myAlertDialogFragment.getDialog() but it's always returning null even once the fragment is displayed

public static class MyAlertDialogFragment extends DialogFragment {

    public static MyAlertDialogFragment newInstance(int title) {
        MyAlertDialogFragment frag = new MyAlertDialogFragment();
        Bundle args = new Bundle();
        args.putInt("title", title);
        frag.setArguments(args);
        return frag;
    }

    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        int title = getArguments().getInt("title");

        return new AlertDialog.Builder(getActivity())
                .setIcon(R.drawable.alert_dialog_icon)
                .setTitle(title)
                .setPositiveButton(R.string.alert_dialog_ok,
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int whichButton) {
                            ((FragmentAlertDialog)getActivity()).doPositiveClick();
                        }
                    }
                )
                .setNegativeButton(R.string.alert_dialog_cancel,
                    new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int whichButton) {
                            ((FragmentAlertDialog)getActivity()).doNegativeClick();
                        }
                    }
                )
                .create();
    }
}

I know I can to it by inflating a layout that contains both a cancel and an ok button, but I rather use the AlertDialog solution if possible