A United Nations procurement official from Ghana, who was a family friend of Kofi Annan and helped bring up his son Kojo, has emerged as a new line of inquiry in the oil-for-food scandal.

Diana Mills-Aryee received Kojo Annan "something less than 10 times" in her office when he was employed by Cotecna, the Swiss company that received a UN inspection contract ultimately worth $10m.

Cotecna offered Kojo Annan a non-compete agreement worth several hundred thousand dollars, one month after it won the business to inspect goods entering Iraq under the United Nations' oil-for-food programme. Cotecna executives also had contacts with Kofi Annan, though the UN secretary general has said he had no influence over the the UN contract.

Investigators retrieved an e-mail exchange from Ms Mills-Aryee's computer in which she told Kojo Annan about her efforts on behalf of Cotecna. In one e-mail dated June 1, 1999, Kojo informed her that he had set up his own consultancy and listed Cotecna as a client. He concluded: "Don't worry, Aunty, your son will structure your early retirement."

The next day, Ms Mills-Ayree sent an e-mail to Kojo Annan revealing contacts with Michael Wilson, a vice president of Cotecna and a family friend of the Annans. She complained that Mr Wilson was unappreciative of her advice on ways for Cotecna to save money on the UN contract. She said she had suggested that Cotecna should seek the same treatment as another inspection company, Saybolt, which had been given extra vehicles by the UN.

Ms Mills-Ayree's actions could be a violation of the confidentiality clause of the UN employment contract that prohibits disclosure of information outside the UN.

The two e-mails are being investigated by the Independent Inquiry Committee on the Oil for Food programme, the special commission headed by Paul Volcker, former chairman of the Federal Reserve.

Ms Mills-Aryee stressed she was never involved in the bidding process on the inspection contract.

However, the Financial Times and Il Sole, the Italian business newspaper, were told by a source other than the IIC that a couple of weeks before her first interview with the IIC, she closed a bank account in Ghana. She transferred the balance of about $10,000 to her New York account with the UN Federal Credit Union, where many UN employees have their accounts.

Investigators have found one payment of about $50,000, made by Cotecna to a separate Ghanaian trust associated with Michael Wilson that registered Kojo Annan as one of its directors.

Ms Mills-Ayree told the Financial Times and Il Sole: "I know nothing apart that Wilson brought Kojo into Cotecna."

Mr Wilson said he had no contacts with the UN Procurement Department and refused to comment further.