Days before President Donald Trump took office, incoming National Security Adviser Michael Flynn blocked a military plan against the Islamic State group that was opposed by Turkey, a country he had been paid more than $US500,000 ($A672,400) to advocate for, the McClatchy news service reports.
According to the report, Flynn declined a request from the Obama administration to approve an operation in the IS stronghold of Raqqa, effectively delaying the military operation.
His reasoning wasn't reported, but Turkey has long opposed US military operations in co-operation with Kurdish forces.
At the time, Flynn had not yet registered as a foreign agent and disclosed that he had been paid to lobby on behalf of the Turkish government. Weeks after his firing, Flynn retroactively registered with the Justice Department.
News about Flynn's activity comes amid intense scrutiny over his and other Trump associates' potential contacts with Russia.
On Wednesday, the Department of Justice named former FBI Director Robert Mueller to be special counsel investigating Russian efforts to influence the US presidential election. Mueller will have sweeping powers, including the right to bring federal charges.
House and Senate intelligence committees are also investigating.
Trump fired Flynn in February on other grounds - that he misled Vice President Mike Pence and other White House officials about his conversations with Russia's ambassador to the US.
McClatchy's reporting reflects previous reports in The New Yorker and other media outlets about Flynn's work on behalf of Turkey.
The military plan against the Islamic State stronghold was eventually approved, but not until after Flynn had been fired.
