A vehicle-mounted Katyusha rocket battery, similar to the one which was likely used to attack the US base in Kirkuk, Iraq on Dec 27, 2019. (via DefenseTalk.com)
As many as 36 Katyusha rockets struck a base in Kirkuk, Iraq which houses American troops yesterday, causing the death of an American defense contractor and wounding several US soldiers. An announcement of responsibility is pending investigation, as both the remnants of ISIS and Iran-linked Shi'a militias are active in the area. However, ISIS has not had the capacity to conduct such a strike for a year, and the attack is just the latest in a string of 12 over the last three months which have been traced to the conglomerate of Iraqi militias known as Popular Mobilization Units, or PMU’s.
The PMU's are integrated into Iraqi security forces, but many of their brigades ultimately take orders from the Iranian Revolutionary Guard Corps (IRGC). Iranian military leaders have repeatedly threatened US bases in the region with Iranian rockets. US Secretary of State Mike Pompeo warned Iran just two weeks ago that any attacks on American troops resulting in American casualties will trigger a US military response.
The deadly attack comes at a precipitous time, after IDF Chief-of-Staff Lt.Gen. Aviv Kochavi warned that a limited but "intense" confrontation with Iran is coming, reiterating Israel's commitment to prevent Iranian entrenchment in Iraq and Syria. There have been hundreds of mostly unclaimed airstrikes against Iranian or Iranian-allied targets in Lebanon, Syria and Iraq over the past six years, and recent intelligence suggests that Iran is using the IRGC and it's PMU proxies to transport and store Iranian missiles in Iraq.
Sources:
https://www.wsj.com/articles/rocket-attack-in-iraq-kills-u-s-contractor-wounds-four-u-s-troops-11577492632
https://www.debka.com/an-american-killed-4-injured-in-heavy-iraqi-shiite-rocket-strike-on-us-k-1-base-near-kirkuk/
https://www.reuters.com/article/us-iran-iraq-missiles-exclusive/exclusive-iran-moves-missiles-to-iraq-in-warning-to-enemies-idUSKCN1LG0WB
https://www.jpost.com/American-Politics/Trump-in-a-corner-after-rockets-kill-US-contractor-wound-forces-612346?fbclid=IwAR1u8NiJ51Ut_p_4TR__WjQbG82FmTqfcypjyXasXFdlpYQTbVrSDJHS_og
https://www.timesofisrael.com/idf-chief-israel-alone-in-the-fight-against-iran-in-syria-iraq/
https://www.i24news.tv/en/news/israel/diplomacy-defense/1577266477-israel-s-army-chief-concerned-over-iranian-activity-in-protest-ridden-iraq
https://www.washingtonpost.com/world/national-security/pompeo-warns-iran-about-trigger-for-us-military-action-as-some-in-administration-question-aggressive-policy/2019/06/18/48bd3be0-9116-11e9-b570-6416efdc0803_story.html
https://www.wsj.com/articles/pompeo-warns-iran-over-rocket-attacks-at-iraqi-bases-11576277357