The Treasury named MPs Amin Sherri and Muhammad Hasan Raad to a terror-related blacklist, saying that Hezbollah uses its parliamentary power to advance its alleged violent activities.
Also placed on the blacklist was Wafiq Safa, a top Hezbollah official close to Hezbollah Secretary General Hassan Nasrallah.
"Hezbollah uses its operatives in Lebanon's parliament to manipulate institutions in support of the terrorist group's financial and security interests, and to bolster Iran's malign activities," said Sigal Mandelker, Under Secretary of Treasury for Terrorism and Financial Intelligence.
The move came as the U.S. steps up pressure on Iran and its alleged "proxies" in the Middle East, including Hezbollah, which Washington accuses of encouraging "terror" attacks.
However, officials stopped short of a threatened sanctions action against Iranian Foreign Minister Mohammad Javad Zarif.
On June 24, Treasury Secretary Steven Mnuchin said Zarif would be added to the sanctions list "later this week," amid rising tensions in the Gulf.
A senior administration official who insisted on anonymity would not confirm that plan.
"We are obviously exploring ... various avenues for additional sanctions on Tehran. Obviously Foreign Minister Zarif is a figure of key interest," she said.
It was the first time the U.S. Treasury had placed Hezbollah lawmakers on its blacklist, which forbid U.S. individuals and businesses with a U.S. branch -- including leading international banks -- from doing business with those sanctioned.
"It is time we believe for other nations around the world to recognize that there is no distinction between Hezbollah's political and military wing," a senior administration official who insisted on anonymity told journalists.
"To any member of Hezbollah considering running for office, know that you will not be able to hide beneath the cover of political office," the official said.
Raad, 64, is the head of the parliamentary bloc of the party and an MP since 1992.
Sherri, 62, is a 17-year Hezbollah veteran of parliament representing Beirut.
Safa, the Treasury said, maintains the group's ties to financiers and allegedly helps arrange the smuggling of weapons and drugs.