The U.S. Treasury Department said four men were sanctioned for effectively acting as "ambassadors" for Hezbollah, which Washington considers a terrorist group. They were acting in Sierra Leone, Senegal, Cote d'Ivoire and Gambia, it said. The sanctions mean the men are effectively cut off from the U.S. financial system and any dealings with U.S. citizens.
The move is part of a multi-year probe that has exposed what the U.S. government says are tight links between South American drug traffickers and Middle Eastern militant groups such as Hezbollah.
The drug traffickers use West Africa, known for its lax law enforcement, as a shipping hub to expand into lucrative markets in Europe and the Middle East. Drug proceeds get laundered through exchange houses in Lebanon and other parts of the Middle East, with some of the funds getting channeled to Hezbollah, Treasury has said.
Hezbollah is a Shi'ite Islamist guerrilla and political movement founded with Iran's help after Israel's invasion of Lebanon in 1982.
Militant groups have found it harder to get money directly from governments in the wake of the September 11, 2001 attacks on the United States, when the U.S. government sharply expanded a crack-down on financing.
U.S. officials say Hezbollah receives money from Iran, which has also been hit with financial sanctions over its nuclear program.
"These actions (against the group) are increasingly important as the funding from (Hezbollah's) traditional patron, Iran, is squeezed by international sanctions," David Cohen, U.S. Treasury under secretary for terrorism and financial intelligence, said in a statement.
The U.S. government first moved against the trafficking network in 2011, designating its alleged leader, Ayman Joumaa, a "drug kingpin," allowing the government to seize his assets. They said the network was doing as much as $200 million a month in business.
They also targeted the Lebanese Canadian Bank, the eighth-largest bank in Lebanon at the time, for allegedly helping the Joumaa network launder money, and last year seized $150 million of its assets.
In the most recent action, the United States imposed sanctions against two Lebanese money exchange houses in April, saying they helped launder funds for the international drug trafficking ring and Hezbollah.