“Over the past few days, we have seen life-threatening attacks in Iraq, including on the United States consulate in Basra and against the American embassy compound in Baghdad,” the White House said in a statement. “Iran did not act to stop these attacks by its proxies in Iraq, which it has supported with funding, training, and weapons.”

The statement added: “The United States will hold the regime in Tehran accountable for any attack that results in injury to our personnel or damage to United States Government facilities. America will respond swiftly and decisively in defense of American lives.”

The statement is part of a larger U.S. pressure campaign on the Islamic Republic that picked up speed last May when President Donald Trump withdrew the U.S. from the multilateral nuclear agreement with Iran. Since then, the U.S. has reimposed sanctions on the country and plans to go ahead with a more crippling set of restrictions in November targeting Iran’s lucrative oil-export revenue. It has simultaneously warned its allies—including those still party to the nuclear accord—that their companies will also be subject to U.S. sanctions if they continue to do business with the Islamic Republic. (The deal is predicated on Iran freezing its uranium-enrichment program in exchange for economic and political benefits.) The goal, the Trump administration says, is to get Iran to change its “behavior” to that of a “normal country.” In other words: no supporting terrorist groups, no interference in regional politics, no ballistic-missile development, no threats against Israel.

The U.S. is developing a new way to weaken Iran.

Although these measures will further hobble Iran’s already moribund economy, they will almost certainly be unable to stop Iran from acting in what it regards as its vital interest in its backyard. Shia Iran’s clerical regime is actively involved in propping up Bashar al-Assad in Syria, supports the Houthis in Yemen, wields considerable influence in Afghanistan, and, of course, dominates Iraqi politics through its funding of Shia parties and its arming of Shia militia. Yet it’s unclear how much Iran actually controls the Shia militia attacking American assets, as the White House statement suggests. Indeed, there are other Shia militia who have attacked Iranian assets.

“We are always trying to understand whether Iran ordered something or whether a militia in Iraq simply inferred that now would be the right time to make a nice gesture toward Iran,” Knights said. “That direct causality and ordering of attacks is something the U.S. is constantly looking out for.”

How will Iraq contain Iran’s proxies?

Take the rocket attack on the U.S. Embassy in Baghdad: It was carried out from an area controlled by Asaib Ahl al-Haq, a Shia militia group. According to newly declassified documents, in 2007 its leader, Qais al-Khazali, gave U.S. forces information on other Shia militia and the extent of Iran’s influence in Iraq.