"The United States will continue to expose any attempts by the Assad regime to meddle in the affairs of its neighbors and further destabilize the region," said Treasury Under Secretary for Terrorism and Financial Intelligence David Cohen.
"We will continue to work with our international partners to ensure that the sovereignty of Lebanon is respected and upheld."
Samaha, 64, who has both Lebanese and Canadian nationality, was minister of information and tourism in the 1990s.
He was officially listed as a "global terrorist" by the US State Department, and the Treasury slapped economic sanctions on him that freeze any assets he holds under US jurisdiction and forbids Americans from doing business with him.
The Treasury said Samaha "reportedly" received the explosives he is accused of transporting from Ali Mamluk, the head of the Syrian National Security Bureau.
"Information available to the US government indicates that in July 2012 Mamluk was involved in a plot with Samaha to conduct bombing attacks against Lebanese political and religious figures in northern Lebanon, and Mamluk provided money and explosives to Samaha for that purpose," the Treasury said.