Is Iran creating its own state within Iraq?

Hamdi Malik and Maysam Behravesh write for the Guardian:

Iraq and its security occupy a central part in the debate about a possible nuclear agreement between Iran and world powers. The Gulf Arab states fear that Tehran, boosted by the relaxation of economic sanctions, will try to expand and consolidate its “hegemonic” grip over the Middle East.

According to this argument, Iranian hegemony will above all affect Iraq, where Tehran seeks to install a government in thrall to it, hindering the formation of a viable democratic system in its western neighbour. The domestic and foreign exponents of this view point to the growing power of Tehran-backed Shia groups fighting the so-called Islamic State (Isis) as proof of attempts to plant an Iranian “deep state” in Iraq, allegedly similar to Hezbollah in Lebanon.