The Defense Ministers of Iraq and Iran have agreed to a memorandum of understanding which aims to increase military cooperation between the two sides, with a focus on fighting against terrorism and cooperation on technical and border security matters.
US officials are likely to object to this agreement, as the US has been presenting Iranian support for the Syrian and Iraqi governments in fighting against ISIS as part of their “destabilization” of the region, and one of the reasons for more US sanctions against them.
That’s an ongoing problem for the US, as the 2003 US invasion and occupation of Iraq installed a Shi’ite-dominated government run by political figures with very close ties to Iran, and they’ve retained those ties despite general US hostility toward Iran.
With the focus of both Iraq and Iran primarily at fighting against ISIS, it’s no surprise the two sides would be cooperating, as they have a natural mutual interest in this fight, with ISIS clear that their territorial ambitions don’t end at the Syrian and Iraqi borders, and would quickly expand into Iran as well, given the opportunity.