U.S. authorities are building a politically explosive case that Hezbollah, the Lebanese militant group, finances itself through a vast drug-smuggling network that links a Lebanese bank, a violent Mexican cartel, and U.S. cocaine users.

Federal prosecutors Tuesday charged Ayman Joumaa, an accused Lebanese drug kingpin and Hezbollah financier, of smuggling tons of U.S.-bound cocaine and laundering hundreds of millions of dollars with the Zetas cartel of Mexico.

The indictment in Virginia results from a continuing investigation by the U.S. Drug Enforcement Administration targeting Hezbollah, which has a bloody history of terror attacks against the United States and Israel.

Now a powerful partner in Lebanon's government, Hezbollah presents itself as a legitimate political party and rejects allegations of terrorism. But Tuesday's case reflects increasing concern that Hezbollah and its ally, Iran's intelligence service, are expanding their presence in Latin America as conflict with the West intensifies over Iran's nuclear program.

Hezbollah allegedly uses the cocaine trade to develop revenue and build foreign networks, according to U.S., European and Israeli officials. In October, the Justice Department charged an Iranian-American resident of Texas and two Iranian intelligence officers with plotting to hire Mexican cartel gunmen to assassinate the Saudi ambassador in Washington.

Acting in February under the Patriot Act, the U.S. Treasury Department publicly identified the Lebanese Canadian National bank of Beirut, Lebanon's eighth-largest bank, as a “financial institution of primary money laundering concern” linked to Hezbollah. Authorities alleged that the bank facilitated the financing of Hezbollah by Joumaa, a 47-year-old businessman who has resided in Colombia.

The DEA described him earlier this year as the hub of a sophisticated operation that has smuggled cocaine from South America to Africa and Europe, and laundered profits via money exchange houses, used-car businesses and other companies in the United States, Latin America, Africa and Southeast Asia.

The indictment unveiled Tuesday focuses on a different piece of the puzzle: U.S.-bound cocaine trafficking.

Joumaa allegedly coordinated the smuggling of at least 85 tons of Colombian cocaine through Central America and Mexico in partnership with the Zetas, the brutal Mexican cartel founded by former commandos, according to the indictment. Between 1997 and 2010, Joumaa's mafia laundered hundreds of millions of dollars for the Zetas and their Colombian and Venezuelan suppliers, regularly picking up southbound bulk cash shipments of $2 million to $4 million in Mexico City, the indictment says.

“Ayman Joumaa is accused of facilitating the shipments of huge amounts of cocaine for the United States while laundering the proceeds all over the globe,” said DEA Administrator Michele Leonhart. “According to information from sources, his alleged drug and money laundering activities facilitated numerous global drug-trafficking organizations, including the criminal activities of the Los Zetas Mexican drug cartel.”

Filed by the U.S. Attorney in the Eastern District of Virginia, the indictment does not mention Hezbollah. But U.S. officials say the alliance with the Zetas was part of the already targeted network linked to the Lebanese militant group.

“The indictment does not reflect all of the information that the government has,” said a Justice Department official. “It's accurate that Treasury's previous statement connected Mr. Joumaa to Hezbollah. The investigation is ongoing.”

The investigation is politically sensitive because views of Hezbollah -- and its alleged involvement in the drug trade -- differ around the world and even in the U.S. government.

The Shiite militia killed hundreds of people in terror strikes in the 1980s and 1990s, from the car-bombing of the U.S. Marine barracks in Beirut to attacks on Jewish targets in Argentina. In recent years, though, Hezbollah has curbed attacks outside of the Middle East, focusing on its bitter military struggle with Israel and growing role in Lebanese politics. The group is seen in Lebanon, the Arab world and parts of the West as a legitimate resistance organization.

As Iran pursues its nuclear ambitions, Hezbollah and Iran are locked in a worsening shadow conflict with the United States and Israel. This week, Hezbollah leaders claimed that they had identified clandestine CIA officers working in Lebanon.

International sanctions have hurt Iran, which helps fund, train and direct Hezbollah. As a result, antiterror officials say the militant group has relied more heavily on longtime ties to criminal rackets involving members of the far-flung Lebanese diaspora. The DEA has pursued several cases in which Hezbollah operatives allegedly teamed up with or taxed Lebanese-connected traffickers of South American cocaine.

The Joumaa case is the biggest so far. The network described in U.S. documents encompasses Joumaa relatives and associates who own money exchanges, stores and other businesses in Colombia, Panama, Lebanon, Benin and the Democratic Republic of the Congo.

Joumaa allegedy has overseen flows of cocaine from Colombia and Venezuela through two smuggling pipelines: north through Mexico to the United States and east through Africa to Europe and the Middle East.

The organization charged its partners in Mexico and elsewhere between 8 percent and 14 percent for using its sophisticated apparatus to launder the huge cash proceeds, the indictment says. It accuses Joumaa of laundering $850 million.

“Hezbollah derived financial support from the criminal activities of Joumaa's network,” says a Treasury Department document that laid out allegations about the Lebanese Canadian Bank in February. “Additionally, LCB managers are linked to Hezbollah officials outside Lebanon. For example, Hezbollah's Tehran-based envoy Abdallah Safieddine is involved in Iranian officials' access to LCB and key LCB managers, who provide them banking services.”

A money exchange house in Joumaa's network used a branch of the Lebanese bank to deposit “bulk proceeds of drug sales” and then wire them to “U.S.-based used car dealers,” the document says. The cars were sold and sent to Africa in suspiciously structured transactions, U.S. officials say.

The Lebanese bank denied the U.S. charges in February. In the wake of the Treasury allegations, however, Lebanon's Central Bank announced that a Lebanese subsidiary of Societe Generale would acquire the assets and liabilities of Lebanese Canadian Bank, which had 35 branches and $5 billion in assets.

Chris Kraul in Bogota, Colombia, contributed to this story.

This story was originally published by the independent, non-profit newsroom ProPublica.