The activities of several vendors obtaining humanitarian aid for Syria for the International Rescue Committee have been halted amid an investigation by the US government into reports of corruption.
The global aid agency, headed by former British foreign secretary David Miliband, is not suspended from US funding, said a spokesman for the US Agency for International Development (USAID).
But the aid agency said it could not disclose whether the organisation was under investigation as reported in some media.
USAID's Office of Inspector General said last week that it had unearthed corrupt practices involving a number of programs operating out of Turkey which provide humanitarian aid to Syria.
"The investigation to date has identified a network of commercial vendors, NGO employees, and others who have colluded to engage in bid-rigging and multiple bribery and kickback schemes related to contracts to deliver humanitarian aid in Syria," it said in a statement.
In response, USAID has halted several aid activities in Turkey over suspicions of fraud and suspended some people and some vendors from getting US funds, officials said.
The agency refuted media reports that the IRC and another leading charity, the International Medical Corps, were among those getting USAID funding withdrawn.
"IRC and IMC have not been suspended," said Sam Ostrander, a spokesman for USAID in Washington, DC.
But he said several humanitarian aid procurement activities have been halted while the system is repaired.
A report in the Times of London said the IRC was under US investigation.
The Inspector General for USAID cannot confirm or deny whether a group is under investigation, a spokesman said.
Not being suspended does not preclude an organisation from being under investigation, however, the agencies said.
A spokeswoman for the IRC in London told the Thomson Reuters Foundation: "We are working openly and collaboratively with USAID to investigate this issue."
The Inspector General's office said several aid agencies have fired staff members due to misconduct it had uncovered.
In January 2016, as a result of the investigation, the IRC fired two staff members from its Turkey office who had accepted money from vendors in exchange for steering contracts to them, the Inspector General's office said.
The IMC said it has laid off 800 employees and fired three others suspected of involvement in the scheme. It also said it is cooperating with the USAID investigation and had opened an investigation of its own.
IMC's aid programs funded by other donors continue, and it is able to distribute medicine already in its warehouse in Turkey, it said.
Another charity, GOAL Syria, said it was cooperating with the investigation and that certain aspects of its program to procure emergency food and other items for Syria have been suspended.
The war in Syria has killed more than 250,000 people though with tens of thousands unaccounted for, some say the death toll may be as high as 400,000.