"We believe his treatment is unjust and unwarranted. We regret that he was convicted and the severity of his sentence," the State Department Spokesperson, Jen Psaki, told reporters.
"We have clearly communicated our position, as we consistently have, to Pakistan, both in public and in private. We continue to raise this issue at the highest levels during discussions with Pakistan's leadership. Our position has long been clear and has not changed," she said.
Afridi provided polio vaccinations in the Pakistani city of Abbottabad as cover for his CIA-backed effort to obtain DNA samples from children at a compound where bin Laden was later killed during a 2011 raid.
He was convicted and sentenced by a Pakistani court to 33 years in prison for treason. The sentence was later overturned and Afridi faces a retrial.
Psaki was responding to questions on the various documents released by the US Government on non-use of vaccination programme by the CIA.