The Iraq oil-for-food inquiry is reviewing new material on Kofi Annan's alleged contact with a firm which won a contract to work for the UN programme.
Mr Annan said he could not recall the alleged exchange
Two newly uncovered memos from the company, Cotecna, suggest the UN head may have known more than he said about the multi-million dollar contract.
Mr Annan has denied prior knowledge of Cotecna's bid for the contract, though his son worked there as a consultant.
An earlier UN report found no evidence that Mr Annan had helped Cotecna.
However, Mr Annan was criticised for failing to look into the possibility of a conflict of interest.
And his son Kojo was found to have "intentionally deceived" his father about his financial relationship with the company.
Cotecna was hired in 1998 by the UN to monitor goods coming into Iraq under the oil-for-food programme.
The first memo from Cotecna describes a meeting between Kofi Annan and Michael Wilson, then a vice-president of the firm, 10 days before the contract was awarded.
It says an executive met the head of the UN "and his entourage" and was told the firm "could count on their support".
The memo, published by the New York Times and later confirmed as authentic by an unnamed Cotecna consultant, was apparently found three weeks ago during a search of the Geneva-based company's archives.
The second memo, also from Michael Wilson but reported by AP news agency, discussed a meeting three days earlier with UN procurement officials to talk about the bid.
The message expressed confidence that the bid would be successful because of "effective but quiet lobbying within diplomatic circles in New York".
It also suggests that Mr Wilson mistakenly believed Mr Annan's approval was required for the bid.
The UN independent inquiry committee said in a statement it would "conduct additional investigation regarding this new information".
"Does this raise a question? Sure," the executive director of the investigation, Reid Morden, told AP.
He said the secretary general would soon be interviewed as part of the investigation.
Salim Lone, a former UN director of communications in Baghdad, told the BBC that the allegations were potentially very damaging for Mr Annan.
"If it is true I think it would be devastating for Mr Annan," he said.
"I don't think he could continue as secretary general. It would be untenable because he has denied quite strongly any knowledge of Cotecna pursuing this contract and he has also set quite high standards for himself."
But Mr Wilson told the New York Times no senior company officials had any recollection of the memos, which appeared to contradict what the company had said.
UN spokesman Fred Eckhard, meanwhile, said he could not confirm that the meeting between Mr Annan and the Cotecna executives took place.
"We spoke to the secretary general who is in Paris today, and he has no recollection of any such exchange," he told AP on Tuesday.
The final version of the inquiry's report is due out in the next few months.