Hardly surprising is it, as Iran would love to extend its territory into Iraq.
They did have that rather nasty war about 10 years ago when the West supported Iraq, so they feel they have a few scores to settle.

Iran is almost certainly supporting alqueda and other extreme groups to achieve its aim.

Not least the fact that they want an Islamic state, rather than a democracy.

NO Islamic states want a democracy (which includes Saudia Arbia)