"Intelligence sources led coalition forces to the location of a suspected Kataib Hezbollah associate believed to be in control of at least one terrorist cell" operating in the southern city of Basra, it said in a statement.
It said the man and three others were detained in operations carried out late Monday and early Tuesday in the northern district of Adhamiyah.
In two other operations in the same area, five more Shiite men were captured with weapons and electronic equipment used to launch improvised rocket-assisted mortars, the military said.
One man detained was allegedly designing websites for Kataib Hezbollah, meaning Hezbollah (party of God) Brigade, to publicise their attacks on Iraqi and US forces.
In a statement on Al-Manar television which is run by Lebanon's Iranian-backed Shiite militant group Hezbollah, Kataib Hezbollah has said its main aim was to drive US and British troops out of Iraq.
Washington has long alleged that Tehran is supporting various anti-US insurgency groups in war-torn Iraq, calling them "Special Groups" or splinter factions once allied with Iraq's Shiite radical leader Moqtada al-Sadr.
The US military said Kataib Hezbollah, while not part of the Special Groups, had since 2005 claimed responsibility for sophisticated attacks and alleged that the group was supported by Iran, receiving funding, logistics and weapons.
Its fighters also receive guidance from Iran's elite Revolutionary Guard Corps, it said.
The New York Times reported in May that Lebanon's Hezbollah had been training Iraqi militiamen at a camp near Tehran, basing its report on US interrogation of four suspects.
