The US State Department had no immediate comment.
Maduro did not give further details, but said the detainee was giving a statement in custody.
He did not provide further details of how Iran was helping, noting he should maintain “silence since we are in a war.”
Iran in May supplied gasoline to Venezuela to ease chronic shortages, triggering alarm bells in Washington as the two countries expand trade relations amid efforts to undermine US sanctions
Though Venezuela has previously purchased weaponry from countries like China and Russia, Maduro's government is mired in a long-running fiscal crisis.
“These actions represent the government’s largest-ever seizure of fuel shipments from Iran,” the US Justice Department said.
Tensions between Iran and the United States increased last year following a series of incidents involving shipping in and near the Middle East Gulf.
Tehran has sent nine oil tankers to its ally Venezuela in recent months.
Virtual embassy to Israel to open next week in lieu of physical presence.