Ambassador Michael McCarthy said he had recently visited several rural counties and "was startled and deeply troubled to encounter multiple county hospitals that received not one penny of what they were promised in the 2022 budget".
He said in a statement received late Monday that some $100,000 was meant to be distributed to hospitals.
Meanwhile, the United States has committed to spending over $40 million to build a laboratory in Liberia, which will require $3-4 million annually from the national government to operate.
"The blocking of resources is so complete that it must be institutional: and the lack of any alarm being raised indicates a syndicate involving players at the legislature, the Ministry of Health, and the Ministry of Internal Affairs" said McCarthy, whose country is a longstanding ally of Liberia.
He also said none of the countryside service centres he visited had received any of their budget allocation for 2022, normally around $13,000.
One such centre, which last received its allocation five years ago, has not printed marriage certificates for four years because the printer had broken, he said.
"It was striking that the further I went from Monrovia, the more elaborate and explicit were the reasons given for the lack of funding from the central government," said the ambassador, whose successor was nominated in March.
"While hospitals went without, and service centres withered on the vine, (Liberia's) 30 senators and the 73 representatives spent $65 million feathering their own nests."
He also lambasted representatives, senators and ministers for receiving annual duty-free imports and for paying lower taxes than average citizens.
"Should the U.S. Congress ask how the elite in Monrovia are treating destitute citizens in the leeward counties, my honest response would have to be, 'those citizens are treated with a neglect that borders on contempt'", McCarthy said.
Graft is endemic in Liberia, with the watchdog Transparency International ranking it 142nd of 180 countries in its 2022 corruption perceptions index.
In December, several hundred Liberians demonstrated peacefully at the call of the opposition to protest government incompetence, as well as President George Weah's alleged indifference to the plight of ordinary Liberians.
Weah will seek a second term in the presidential election on October 10.
Fighting corruption was one of his major campaign promises in last election, but last year the United States accused three of his close allies of corruption and imposed sanctions on them.
In September Weah accepted their resignations.
US Envoy Blasts Liberia's Performance
MONROVIA - Washington's ambassador to Liberia has accused lawmakers of "buttering their own bread" and "feathering their own nests" while underfunding hospitals and service centers, leaving rural citizens "destitute."