In an unprecedented step to ramp up pressure on Tehran, the Trump administration is planning to designate Iran’s Revolutionary Guard a “foreign terrorist organization.” The move is expected to further isolate Iran and could have widespread implications for U.S. personnel and policy in the Middle East and elsewhere.

The Trump administration has escalated rhetoric against Iran for months, but this will mark the first such designation by any American administration of an entire foreign government entity. Portions of the Guard, notably its elite Quds Force, have been targeted previously by the United States.

Officials informed of the step said an announcement was expected as early as Monday.

Two U.S. officials and a congressional aide confirmed the planned move. They were not authorized to discuss the matter publicly and spoke on condition of anonymity. Iran’s foreign minister, Mohammad Javad Zarif, seemed to anticipate the designation, saying in a tweet Sunday aimed at President Donald Trump that Trump “should know better than to be conned into another US disaster.”

This would be just the latest move by the Trump administration to isolate Iran. Trump withdrew from the Obama administration’s landmark nuclear deal with Iran in May 2018 and in the months that followed, reimposed punishing sanctions including those targeting Iran’s oil, shipping and banking sectors.

The Revolutionary Guard designation, planning for which was first reported by The Wall Street Journal, comes with sanctions, including freezes on assets the Guard may have in U.S. jurisdictions and a ban on Americans doing business with it or providing material support for its activities.

Although the Guard has broad control and influence over the Iranian economy, such penalties from the U.S. may have limited impact. The designation, however, could significantly complicate U.S. military and diplomatic work, notably in Iraq, where many Shiite militias and Iraqi political parties have close ties to the Guard. And in Lebanon, where the Guard has close ties to Hezbollah, which is part of the Lebanese government.

Without exclusions or waivers to the designation, U.S. troops and diplomats could be barred from contact with Iraqi or Lebanese authorities who interact with Guard officials or surrogates.

The Pentagon and U.S. intelligence agencies have raised concerns about the impact of the designation if the move does not allow contact with foreign officials who may have met with or communicated with Guard personnel. Those concerns have in part dissuaded previous administrations from taking the step, which has been considered for more than a decade.

It was not immediately clear whether the designation would include such carve-outs.

In addition to those complications, American commanders are concerned that the designation may prompt Iran to retaliate against U.S. forces in the region, and those commanders plan to warn U.S. troops remaining in Iraq, Syria and elsewhere of that possibility, according to a third U.S. official. This official was not authorized to discuss the matter publicly and spoke on condition of anonymity.

Aside from Iraq, where some 5,200 American troops are stationed, and Syria, where some U.S. 2,000 troops remain, the U.S. 5th Fleet, which operates in the Persian Gulf from its base in Bahrain, and the Al Udeid Air Base in Qatar, are potentially at risk.

A similar warning is also expected from the State Department of possible Iranian retaliation against American interests, including embassies and consulates, and anti-American protests, the first two U.S. officials said. Similar alerts were issued at the start of the Iraq War in 2003 and more recently when the Trump administration announced it would recognize Jerusalem as Israel’s capital.

Despite the risks, Iran hard-liners on Capitol Hill, such as Sens. Tom Cotton, R-Ark., and Ted Cruz, R-Texas, and elsewhere have long advocated for the designation. They say it will send an important message to Iran as well as deal it a further blow after Trump pulled out of the 2015 nuclear deal and reimposed economic sanctions.

Secretary of State Mike Pompeo and national security adviser John Bolton have taken up the call and have in recent months spoken stridently about Iran and its “malign activities” in the region.

Pompeo has made clear in public comments that pressure on Tehran will only increase until it changes its behavior. Just last week, Pompeo’s special representative for Iran, Brian Hook, accused Iran and its proxies of being responsible for the death of 608 U.S. troops in Iraq between 2003 and 2011. He cited newly declassified Defense Department information for the claim, which is expected to be used in the justification for the Guard designation.

“Secretary Pompeo will continue to use all the tools at our disposal to press the regime to change its destructive policies for the benefit of peace in the region and for the sake of its own people, who are the longest-suffering victims of this regime,” Hook said, in an indication that new action is coming.

The department currently designates 60 groups, such as al-Qaida and the Islamic State and their various affiliates, Hezbollah and numerous militant Palestinian factions, as “foreign terrorist organizations.” But none of them is a state-run military.

Once a designation is announced by the secretary of state in coordination with the Treasury secretary, Congress has seven days to review it. If there are no objections, it then will take effect.