Iran has multiplied its support for the Lebanese militant group Hezbollah to more than $700 million a year, according to US estimates.

The new figure is more than three times as much as previous estimates of funding for the group.

Speaking at the Foundation for Defence of Democracies (FDD) in Washington on Tuesday, the US Treasury under-secretary for terrorism and financial intelligence, Sigal Mandelker, condemned the Iranian government’s behaviour on several fronts, including funding illicit activities and supporting terrorism.

She also referred to US-UAE co-operation and the efforts last month to uncover and break up a secret financial network sending money to Iran’s revolutionary guard (IRGC) and Quds force.

Ms Mandelker accused the Iranian regime of using shell and front companies, and forging documents to conceal its tracks in order to “fund terrorists, support weapons of mass destruction proliferation or exploit its own people through corruption and human rights abuses”.

The US under-secretary said: “Iran provides upwards of $700 million a year to Hezbollah.” That figure is more than triple the $200m previously estimated by the US before Hezbollah’s became embroiled in the Syrian civil war.

Hanin Ghaddar, a fellow at the Washington Institute for Near East Policy, told The National that the new figure is significant because it represents the “first time a US official pins down such a number.” The expert tied the large increase in Iran's budget to Hezbollah, directly to its regional mission, and not its Lebanese activities.

“Funding for Hezbollah’s social services network [in Lebanon] has decreased over the past 6 years, as the budget for its regional operations kept climbing up” Ms Ghaddar said.

The increase covers Hezbollah’s “mission in recruiting, training, advancing its weaponry and leading the Shi’a Militias – mainly in Syria”.

Ms Mandelker, a former prosecutor at the department of justice, accused Iran of undermining the international financial system. She said Iran’s central bank had a direct role in directing the terrorist funding activities. “What is all the more remarkable about this activity is that we are seeing Central Bank of Iran complicity in Quds Force financing,” she said, referencing the foreign wing of the IRGC.

She praised UAE-US efforts to break up a financial network funding the IRGC. “We took action with our partners in the UAE to designate this network and shut it down” she said, urging other countries to follow suit. “The UAE also sent a very strong message that these exchanges and the Quds force are not welcome there, designating individuals and entities involved in this network and cutting their access to the UAE’s financial system” she said.

Ms Mandelker said: “Iran’s central bank governor, other Central Bank of Iran officials and the Quds force team up to take advantage of Iraq’s banking sector in order to surreptitiously move funds on behalf of Quds and Hezbollah.” And in Yemen, besides sending ballistic missiles to the Houthis, she said Quds printed “counterfeit Yemeni bank notes, potentially worth hundreds of millions of dollars, to support Iran’s destabilising activities”.

She condemned the Iranian regime's clampdown on freedom inside Iran, “restricting access to satellite services, blocking access to social media sites and apps, and imposing other Internet restrictions”.

Ms Mandelker also mentioned Iran’s hacking activities, through the “Mabna Institute, targeting 22 countries, including Germany, Italy, and the United Kingdom, as well as our Asian partners such as Japan and South Korea. The institute conducted massive, co-ordinated cyber intrusions into the computer systems of over 300 universities worldwide, including 144 institutions based in the United States.”

After America's targeting of Iranian airlines and front companies in Turkey, Ms Mandelker said that “since the onset of the Syrian civil war, Mahan Air and other designated Iranian commercial airlines such as Caspian Air, Meraj Air, and Pouya Air have routinely flown fighters and material to Syria to prop up the Assad regime”.

“People do not go on vacation to Syria” she said.

Ms Mandelker urged international action in designating these actors and activities linked to terrorism funded by Iran in the eyes of the US, and warned of targeting of those who do business with those networks globally.

But as far as the impact of the US strategy of imposing sanctions on Hezbollah is concerned, Ms Ghaddar questioned the degree of damage it is inflicting on the party. “The US sanctions bother Hezbollah only in the sense that they make their finances more complicated but they have not stopped the funding as Iran still uses the air and land corridors to transfer the money, mostly in cash,” she said.

“Hezbollah’s economy is a cash economy that’s why sanctions won’t seriously harm it, albeit being a nuisance” Ms Ghaddar continued.

For Hezbollah, it largely depends on its allies and business community for moving money. The US should go after those “enablers,” argued the expert, in “a way that would make them reconsider”.