Recent attacks and attempted terrorist strikes in Europe, Africa, the Middle East and southeast Asia have all been linked to either Hezbollah or Iran's Quds Force, an elite unit within the the country's special Revolutionary Guard Corps, State Department counterterrorism officials note.
That resurgence has only been bolstered by the group's increasing role in the three-year civil war in Syria.
Hezbollah is one of many Islamic militant groups that have streamed into Syria, where opposition forces are fighting to topple longtime leader Bashar Assad.
Amid the chaos of the Syrian uprising, Hezbollah fighters have begun transporting weapons to the Shiite-backed Assad regime. They have also been accused by Jerusalem of smuggling weapons and supplies through the country and into occupied territories surrounding Israel.
Last month, Israeli fighters launched a series of airstrikes inside Syria, targeting suspected Hezbollah fighters moving arms and equipment bound for Israel.
On Wednesday, Brig. Gen. Salim Idris, the top commander for the Free Syrian Army (FSA), gave the terror group 24 hours to clear out of Syria or risk attacks from the country's rebel forces.
The FSA is the largest and most organized force within the Syrian opposition, which are battling to oust Assad from power.
Idris told Al-Arabiya that if the terror group does not withdraw its fighters from the country, "we will take all measures to hunt Hezbollah, even in hell.”
That increasing tension between Islamic radicals and Syrian rebels comes as animosity between the Sunni-backed opposition and the country's ruling Alawite population, a strain of Shiite Islam the Assad family practices, in western Syria are also reaching a boiling point.
The result is a prolonged civil war as Sunnis and Alawites square off to fill the power vacuum in the country, mirroring the bloodshed seen in post-Saddam Hussein Iraq, according to Defense Secretary Chuck Hagel.
"The conflict in Syria is intensifying and becoming more sectarian. The possibilities of state fragmentation are increasing, as are the risks of extremism and proliferation," Hagel said in a speech in Washington earlier this month.
The Pentagon, in recent years, has warned Congress on Hezbollah's increasing reach into South America, leveraging partnerships with countries like Venezuela and others in the region.
The group has been actively strengthening its ties to transnational criminal groups in South America and are working to expand ist influence in the region, according to Department of Defense leaders.
“Iran is very engaged in the region,” former Southern Command chief Gen. Douglas Fraser told members of the Senate Armed Services Committee last year.
Iranian terror groups like Hamas and Hezbollah are involved in a number of “illicit activities” likely tied to the regional drug trade, Fraiser said at the time.