Giant posters on the streets of Beirut's southern Shiite suburbs display an armed Hezbollah fighter in uniform, holding the group's yellow banner and Lebanon's national flag, along with phone numbers where supporters can make donations to the Shiite guerrilla force.

Hezbollah's calls for donations have intensified in past months as the group and its main backer Iran come under increasing financial pressure under sanctions from the Trump administration.

Washington has imposed sanctions on the militant group for decades. But a new wave this year appears to be more serious about targeting Hezbollah's top leadership as well as businessmen and companies that Washington says are funding the group. The latest hit came Oct. 15, when U.S. Attorney General Jeff Sessions designated Hezbollah as one of five groups considered top transnational organized crime threats.

Iran, facing its own financial crises, has also reportedly cut back on funding for Hezbollah and Shiite militias it supports in Iraq. Iran touts itself as the leader of the so-called "Axis of Resistance," grouping Syria's Bashar al-Assad, Shiite militias in Iraq, Hezbollah in Lebanon and Shiite gunmen in Yemen known as the Houthis.

The U.S. State Department said in July that Iran has spent over $16 billion since 2012 supporting Assad and its proxies in Iraq and in Yemen, and it also gives $700 million a year to Hezbollah. It has also given the Syrian regime $4 billion in lines of credit, it says.

Hezbollah's budget has already been hurt ever since it became heavily involved in Syria's civil war in 2013, sending fighters to back Assad's forces and helping turn the conflict in his favor. An estimated 2,000 of its fighters have been killed and thousands more wounded, some with permanent disabilities. That only adds to the costs, since the group pays stipends to families of "martyrs" and provides health care for fighters.

Recently, its leadership started to publicly acknowledge the strain. "I won't say that the sanctions will not have an effect ... They will have an effect for sure," Hezbollah leader Sheikh Hassan Nasrallah said in a speech in August. He vowed the sanctions won't diminish the group's power. "We have the strength, infrastructure and human resources to get through these difficulties, God willing," he said.

A Lebanese citizen who has relatives in the group said it has pulled back some fighters in Syria, though it maintains its presence in eastern Deir el-Zour province and in the south, where fighting continues with Daesh, and in Quseir, a town near the border with Lebanon that has been a Hezbollah stronghold for five years.

Despite the tightening, the group hardly seems to be diminished from its status as the strongest fighting force in Lebanon — and one of the strongest in Syria — boasting an arsenal of rockets and a powerful political structure. Even if other funding streams are under strain, Hezbollah can still count on public contributions, which stream in through tens of thousands of metal donation boxes placed in shops, streets, mosques and schools in predominantly Shiite areas of Lebanon.

Its patron Iran, meanwhile, is facing deep economic woes. President Donald Trump withdrew the United States from the nuclear accord with Iran, although the United Nations has repeatedly acknowledged Tehran was living up to the terms of the deal. Trump said he wanted stricter terms to limit Iran's ballistic missile program, curtail its regional influence and forever limit its nuclear activities.

Another ally of Iran, the Yemeni rebels known as the Houthis, are also preparing for difficult times, especially as their opponents, a Saudi-led coalition, besieges the port of Hodeida, a major source of income for the group. The rebels have sharply increased taxes on merchants and businesses.

Iranian-backed militias in Iraq are buffered to an extent from any financial crunch because they also get funding from the Baghdad government, which is nominally a U.S. ally. The militias are part of the government-sanctioned paramilitary group known as the Popular Mobilization Forces, with some 100,000 fighters, who get salaries and equipment from the state.