On July 1 the New York Times headlined: Iraq Cracks Down on Iran-Backed Shiite Militias. Nowhere does the article under that headline provide any facts which support the claim that those militia are backed by Iran. Those militia are allegedly Shia and that is enough to call them "Iran-backed".
Today the Washington Post headlines: Weapons prove Iranian role in Iraq, U.S. says. But the article contains no, that is zero, evidence for that claim. It says that:
Jeffrey[, the U.S. ambassador to Iraq,] provided details of the forensic testing after Gen. Lloyd Austin, commanding general of U.S. forces in Iraq, declined to do so earlier in the day.
But the article does not say or explain what "details of the forensic testing" the ambassador provided. Instead it mentions old U.S. assertions from 2009 and from 2008 and it trots out the old false meme of "explosively formed projectile” found in Iraq as coming from Iran. It also quotes an "expert" from the Israel Lobby who, of course, blames Iran for everything between sunrise and sundown.
Both articles, while using the claim of Iranian involvement in their headlines, do not provide any news at all with regard to Iranian connections to groups in Iraq. Their sole purpose seems to reenforce the meme by repeating it over and over.