Iraq and Iran signed a memorandum of understanding expanding military cooperation between the countries on Sunday in Tehran, in a sign of strengthening ties between the historic rivals.

The agreement covers a wide range of topics within the greater realm of national security, specifically in areas to fight terrorism and extremism, border security, training, logistics, and ‘technical and military support,’ the Iranian news agency IRNA reported.

Defense ministers Brigadier General Hossein Dehqan of Iran and Major General Erfan al-Hiyali chaired the event, holding a press conference following the signing to speak about the “deepening and expanding of defensive cooperation between the two countries.”

Such an agreement is sure to raise concerns from the United States and others involved in the international community who worry over growing Iranian influence in Iraq. Relations between the formally bitter enemies have improved following the 2003 removal of dictator Saddam Hussein in Iraq. Since Hussein’s removal, the Shi’ite Iraqi majority have installed Shi’ite leaders throughout the Iraqi government and military.

Iran has taken a very active role in the campaign against the Islamic State in Iraq, to include through the use of Shi’ite militias under the direction and support of members of Iran’s covert action wing of the Iranian Revolutionary Guard Corps, who advise these militias. Called “Popular Mobilization Units” or “Popular Mobilization Forces” (PMF), they are ostensibly an arm of the Iraqi military to organize Shi’ite militias in the country against ISIS. There have been accusations of sectarian abuses against Iraq’s Sunni minority at the hands of the PMF.

The PMF were used in the Battle of Mosul, but the United States specifically did not become involved in PMF operations despite its wider support for the Iraqi military and federal police.

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The Trump administration has made it a point to be vocal over Iranian influence throughout the region, citing their “malign activities across the Middle East,” as part of the justification for the newest round of economic sanctions against the regime.

Quds Force commander Qassem Soleimani reportedly gave a speech last week extolling the efforts of Iranian forces in the Battle of Mosul, citing it as a victory for Iran. While the contribution by the PMF in the fight for Mosul was apparently minor—the Iraqi army and police bore the brunt of the fighting—it has not stopped the propagandizing effort by the Iranian government from attempting to show solidarity and drive further influence within the Iraqi government and the country itself.

Image By Mstyslav Chernov at https://commons.wikimedia.org/w/index.php?curid=54029665