[gtkmm] Accel group on buttons?

[praca_lodz op pl]

Hello,
  In my application I would like to activate buttons with 
e.g. F1 Button. How do I do that? AFAIK Mnemonics can be only one printable letter (Correct me if I'm wrong).
  I fiddled around with AccelGroup of toplevel window but all I got 
was:
Gtk-WARNING **: gtkwidget.c:3075: widget `gtkmm__GtkButton' 
has no activatable signal "F1" without arguments"

The above result is because of code:
button->add_accelerator("F1",
                                 w->get_accel_group(),
                                 gdk_keyval_from_name( "F1"),
                                 Gdk::RELEASE_MASK,
                                 Gtk::ACCEL_MASK );

(w is toplevel window)

Thanks in advance,
  Radosław Grzanka