Washington, Aug 5 (IANS): Investigators working for special counsel Robert Muller have asked the White House for documents on former National Security Adviser Michael Flynn as they examine whether he was secretly paid by the Turkish government to lobby against a critic of Turkish President Recep Tayyip Erdogan.

Investigators asked the White House for documents related to Flynn's lobbying and questioned witnesses about whether he was paid by the Turkish government, the New York Times reported. 

The document request was not a formal subpoena. The document request is the first known instance of the special counsel asking the White House to hand over records. 

It also shows that the special counsel probe has expanded into an examination of Flynn's financial deals, beyond disclosures about his conversations and business arrangements with Russian officials, the Times reported.

Flynn's former lobbying firm, the Flynn Intel Group, was paid $530,000 to represent Ekim Alptekin, a Turkish businessman, during the final months of the US presidential campaign, according to foreign agent registration paperwork filed with the Justice Department. 

But the contract ended in mid-Novermber 2016, around the time that Flynn was announced as President Donald Trump's first National Security Adviser. Flynn was forced to resign in February after it was reported that he misled Vice President Mike Pence about the nature of his phone calls with the Russian Ambassador to the US, Sergey Kislyak.

While Mueller steps up his investigation into allegations of Russian interference in 2016 US presidential election, Trump again angrily denied that his campaign team colluded with the Kremlin. At a campaign rally in West Virginia on Friday, he dismissed the allegations and investigation as "fake news".

Flynn declined to comment on the New York Times report, while Trump's special counsel Ty Cobb stressed that the White House was cooperating with the probe.

"The White House will not be discussing any specific communications with the Special Counsel out of respect for the Special Counsel and his process. Beyond that, as I have stressed repeatedly, we continue to fully cooperate with the Special Counsel," Cobb told the Hill magazine.