The unit is tasked with providing weapons, equipment and training to radical militant groups affiliated with the Lebanese terrorist organization around the world, according to a department statement issued Thursday.
Most recently, Unit 1800 members have been actively supporting militants looking to destabilize the democratic government in Iraq.
The new round of sanctions are designed to curb Hezbollah's "alarming reach outside Lebanon," David Cohen, head of the Treasury department's counterterrorism office, told reporters Thursday.
Under the new sanctions, members of Unit 1800 and other Hezbollah leaders and facilitators are banned from receiving any material support from U.S. citizens, and any assets located in U.S. territories have been frozen as a result.
The move is another step in Washington's efforts to "disrupt [Hezbollah's] global supply network" and "expose what they have been engaged in" in Iraq, Syria elsewhere, Cohen told reporters during a conference call on Thursday.
The group's overseas operatives will "no longer behave with impunity" as a result of the new sanctions, Cohen added.
Hezbollah senior leaders Muhammad Kawtharani, Muhammad Yusuf Ahmad Mansur, Muhammad Qabalan and Khalil Harb were all identified as targets of the Treasury Department sanctions.
Counterterrorism officials at Treasury have identified Kawtharani as one of the group's senior leaders in Iraq, responsible for "training, funding, political, and logistical support to ... Shi'a insurgent groups," according to the department statement.
"Over the last year, Kawtharani has assisted in getting fighters to Syria to support the Assad regime," according to department officials.
Harb, according to department officials, was a former leader of Unit 1800 and coordinated terrorist attacks inside Israel before being moved to Yemen.
In Yemen, Harb oversaw money transfers and other funding activities flowing from Saudi Arabia and the United Arab Emirates to support extremists in that country,
Mansur and Qabalan were members of the unit's clandestine cell in Egypt, responsible for targeting tourist destinations and other so-called soft targets in the country for attack.
Mansur spent 15 years in prison in Egypt after being convicted of his role in the tourist site plot in 2009, but he was last spotted in Lebanon attending a Hezbollah rally with several of the group's senior leaders, according to the department.
Qabalan was also convicted in absentia for his part in the planned Egypt attacks, but he is now suspected of leading a separate "Hezbollah covert cell" somewhere in the Mideast.