When the Iranian regime demanded a Lebanon cease-fire clause in the memorandum of understanding with the U.S., it was a clever move. In exchange for ending its stranglehold on the Strait of Hormuz, the regime sought to end the assault on Iran and to protect Hezbollah, its most powerful terror proxy, from Israel's efforts to dismantle it.
The clause placed Israel, which didn't have a hand in the negotiations, in a painful bind. Israelis are under daily assault by Hezbollah. If they don't respond, they lose momentum in their northern front, while dozens of soldiers fall on the battlefield. If they do respond, they risk upending the high-stakes diplomacy between the U.S. and Iran. More pointedly, they risk losing the support of Washington.
The memorandum places a valued American ally in an impossible position. It also ignores Iran's direct role in the Hezbollah violence.
Hezbollah's decision to enter the war on March 2 in retaliation for the killing of Iranian Supreme Leader Ayatollah Ali Khamenei has proved disastrous for the terror group. Hezbollah was already weakened by more than two years of war with Israel. The Israeli exploding-beeper operation, the killing of longtime leader Hassan Nasrallah, and the Israel Defense Forces' tenacious efforts to weaken the group have paid off. Yaakov Amidror, a former Israeli National Security Council adviser, estimates the terror group has lost roughly 75% of its prewar strength and firepower.
The Iranian regime wants to stanch the bleeding. This goes beyond supplying the group with money and weapons. The Islamic Republic is now the backbone of Hezbollah's command structure.
Iran has deployed as many as 150 Islamic Revolutionary Guard Corps officers to Lebanon. After Operation Epic Fury, the IRGC's goal was to create a decentralized structure that could survive Israeli attacks. The IRGC organized Hezbollah fighters into smaller, compartmentalized cells.
The IRGC's presence in Lebanon became clearer after Israel began targeting its personnel. Israel in March struck a room in the Ramada Plaza hotel in Beirut, killing at least four IRGC officers. They had checked into the hotel using authentic Lebanese passports under aliases. Officials found additional IRGC reservations under Lebanese passports at another hotel in Beirut. The bookings were arranged through an apparent front company called Power, a limited partnership founded in 2012, according to Alhurra, a U.S. government-funded Arabic-language media network.
According to the IDF, those killed were members of the Quds Force, the IRGC's extraterritorial arm, including the Lebanon branch's financial officer, the intelligence chief in Lebanon, a leader in the Palestine branch and a lower-ranking intelligence operative in the Lebanon Corps.
Other IRGC officers targeted by Israel in Lebanon in March reveal the extent of IRGC entrenchment. One was chief of staff at the Quds Force's Lebanon Corps and was responsible for helping Hezbollah rebuild its military capabilities. Another commanded the IRGC's missile unit within Hezbollah.
Lebanon's government has acknowledged the problem. Prime Minister Nawaf Salam this spring said that the IRGC was commanding Hezbollah operations. His government ordered "measures to prevent any military or security activity carried out by members of the Iranian Revolutionary Guard in Lebanon, in preparation for their deportation." While some IRGC officials left Lebanon, a small contingent reportedly remained.
Open-source reporting and Iranian hacktivist leaks indicate that there are likely three Quds Force units in Lebanon. It appears that Unit 700 handles transportation and weapons transfers, Division 8000 supports production and supply and Unit 190 plays a key role in weapons smuggling.
So, when the Iranian regime halts negotiations with the U.S. or closes the Strait of Hormuz in response to clashes in Lebanon, it is playing U.S. negotiators. Tehran is running the show in Lebanon, and when the Israelis respond, the regime cries foul.
Weekend negotiations between the U.S. and Iran included talks about the violence in Lebanon. This is important. But the benefits of any cease-fire agreement will be negligible if the U.S. team doesn't tackle the Iranian role in directing and coordinating the attacks designed to derail diplomacy.
The memorandum of understanding will be a failure if it creates conditions for a Hezbollah recovery. If Washington wants to break Iran's grip on Lebanon, it has a clear path forward: Help Beirut enforce its ban on IRGC activity, expel all Iranian personnel operating in Lebanon, and investigate the fraudulent use of Lebanese passports and the local IRGC facilitation networks. The U.S. could also impose sanctions on individuals and entities enabling the IRGC in Lebanon.
Finally, until Hezbollah's attacks cease and Iran is out of Lebanon, the U.S. should greenlight Israeli reprisals. Washington can take advantage of Israeli pressure on Hezbollah to get a better deal.
Mr. Schanzer is executive director and Mr. Sharawi a senior research analyst at the Foundation for Defense of Democracies.