Reuters on Wednesday quoted two Iraqi security sources who revealed Secretary of State Mike Pompeo issued warnings about Iran-backed Shiite militia threatening U.S. bases in Iraq with missiles when he paid a surprise visit to Baghdad on May 7.

Pompeo reportedly warned the Iraqi government to keep those Shiite forces at bay, or else the U.S. military would deal with them:

“The message from the Americans was clear. They wanted guarantees that Iraq would stop those groups threatening U.S. interests,” a senior Iraqi military source with knowledge of Pompeo’s trip said. “They said if the U.S. were attacked on Iraqi soil, it would take action to defend itself without coordinating with Baghdad.” The U.S. State Department declined to comment on the details of Pompeo’s discussions. He had said after the trip: “We don’t want anyone interfering in their country (Iraq), certainly not by attacking another nation inside of Iraq.” The second Iraqi security source said: “Communications intercepted by the Americans showed some militia groups redeployed to take up suspicious positions, which the Americans considered provocations.” He said the Iraqis were told that any threat from the groups “would be dealt with directly by the Americans with force.”

The Shiite militias in question are not rogue outlaw groups, but official elements of the Iraqi military collectively known as “Popular Mobilization Forces” (PMF). They operate with a high (and troubling) degree of autonomy and enjoy political support from Shiite Iraqi politicians politically aligned with Iran. There are at least fifty different militia groups operating under the PMF designation with about 150,000 fighters in total.

Sunni Muslims living in Iraq have been worried about the Shiite militias for a long time. Apprehension about their activities was one of the reasons the Islamic State was able to get established in Iraq so easily. Conversely, the Shiite militias gained prestige and political support by fighting against ISIS.

After the fall of the ISIS “caliphate,” the Shiite militias began establishing what looks disturbingly like a parallel government in numerous towns, to the dismay of Sunnis living there and the even greater dismay of Sunnis forced to leave because the PMF confiscated their property. Critics of the PMF compare them to organized crime rings or the warlords of Libya.

The degree of control Baghdad can exert over the PMF is uncertain, a problem Pompeo highlighted during his visit by publicly urging the Iraqi government to “get all of those forces under Iraqi central control.”

Representatives for some of the militia groups insist they have no plans to attack American forces. Reuters quoted some analysts who believe the missile movements detected by the United States are a “symbolic threat” rather than preparations for a real attack.

The U.S. State Department instructed all non-essential, non-emergency staff to leave Iraq immediately on Wednesday. The United Kingdom on Thursday placed personnel in Iraq, Saudi Arabia, Kuwait, and Qatar on an increased alert level due to security threats from Iran and its proxy forces. A source in the British government told Sky News the Iranians are contemplating plausibly deniable terrorist attacks and sabotage through proxies to damage U.S. and allied interests without triggering all-out war.

Germany and the Netherlands suspended military training operations in Iraq on Wednesday, citing the U.S. warning of an increased terrorist threat from Iran. German officials described the suspension as a temporary precaution and said German intelligence sees no indication of an imminent attack by Iran or its allies.