Panetta is meeting with military and political leaders in Brazil, Colombia and Chile to reaffirm the U.S. commitment to help with common defense challenges, a Department of Defense report said.
One of the major challenges, the report indicated, involves potentially violent extremist organizations and Iran's encroachment into Central America, South America and the Caribbean.
"I hope we can work together to make sure that all the steps are taken to ensure that anything that encourages terrorism can be fought against," Panetta said.
Air Force Gen. Douglas M. Fraser, commander of the U.S. Southern Command, last month presented written testimony to the Senate Armed Services Committee containing a thoroughly detailed account of Hezbollah's activities in the region and Iran, the report said.
Fraser's testimony said Iranian President Mahmoud Ahmadinejad visited the region six times in as many years, and Iran consistently makes overtures to countries in the region in an attempt to circumvent international sanctions.
"We take Iranian activity in the hemisphere seriously and we monitor its activities closely," Fraser said. "We do see evidence of international terrorist groups benefiting from the intertwined systems of illicit trafficking and money laundering in our AOR [area of responsibility]."
In South America, much of the funding for Hezbollah comes from charitable donations, along with drug trafficking and trading in counterfeit and pirated goods, Fraser said.
"In addition to Hezbollah supporters throughout South America, the region is home to a small number of violent extremist organizations," Fraser said. "We remain vigilant for the potential radicalization of homegrown extremists."