Washington has offered up to $7 million for information leading to the detention of Talal Hamiyah, head of Hezbollah's foreign operations, and up to $5 million for Fu'ad Shukr, a top Hezbollah military operative.
The move on Tuesday came as the Trump administration prepared to unveil a strategy to step up pressure on Hezbollah's main backer Iran. Nicholas Rasmussen, the head of the U.S. National Counterterrorism Center, blamed the group for a series of attacks around the world.
"These accusations from the American administration against Hezbollah and its mujahideen are rejected and void ... They will not affect the work of the resistance at all," a senior Hezbollah official told Reuters.
The official, who declined to be named, said the U.S. threat came as a reaction to Hezbollah's recent gains in the region.
Shi'ite Hezbollah has played a major role in backing President Bashar al-Assad in the six-year Syrian war. It has sent thousands of its fighters into Syria, helping the Damascus government recover territory from rebels and militants.
Hamiyah has been on the U.S. State Department's foreign terrorist list since 2015 and Shukr was added in 2013.
Washington named Hezbollah as a foreign terrorist organization in 1997.