Inadequate oversight of that assistance could enable Al-Shabaab to siphon off some of that money.
That lapsed compliance with the so-called Leahy Law spanned several months in 2014 and again in a period spanning 2016 and 2017.
The law in question requires the US State Department and Pentagon to determine whether potential aid recipients carry out extrajudicial killings.
The State Department's Africa Bureau is failing to ensure that US funding for the Somali government is not diverted to Al-Shabaab terror group, the department's watchdog unit warned on Monday.
"The bureau had not established policy and procedures for identifying, assessing and mitigating terrorist financing risks for its programmes in countries where terrorist organisations, such as Al-Shabaab and Boko Haram, operate," the State Department's Office of Inspector General said.
In a 34-page report assessing the bureau's foreign assistance management, a team of inspectors cited the example of $66 million paid as cash stipends to members of the Somali National Army during the past seven years.
Inadequate oversight of that assistance could enable Al-Shabaab to siphon off some of that money intended for 6,509 Somali government soldiers, the report suggested.
In addition, inspectors found that the Africa Bureau continued paying the soldiers' stipends while failing to comply with a US law that prohibits State Department assistance to foreign military units that have not been screened for human rights violations.
That lapsed compliance with the so-called Leahy Law spanned several months in 2014 and again in a period spanning 2016 and 2017, the report said.
"Furnishing security assistance without conducting Leahy vetting raises the risk that funds could be provided to individuals who have committed gross violations of human rights or are otherwise ineligible for assistance," the report stated.
The law in question -- named for its primary author, Democratic Senator Patrick Leahy -- requires the US State Department and Pentagon to determine whether potential aid recipients carry out extrajudicial killings, enforced disappearances and rapes.
The State Department's own worldwide report on human rights found in 2016 that Somali government forces abused civilians. Somali authorities "generally did not investigate abuse by police, army or militia members," the 2016 evaluation added. "A culture of impunity was widespread."