A spokesman for Mr. Clinton said the former president knew that Mr. Giustra had mining interests in Kazakhstan but was unaware of “any particular efforts” and did nothing to help. Mr. Giustra said he was there as an “observer only” and there was “no discussion” of the deal with Mr. Nazarbayev or Mr. Clinton.

But Moukhtar Dzhakishev, president of Kazatomprom, said in an interview that Mr. Giustra did discuss it, directly with the Kazakh president, and that his friendship with Mr. Clinton “of course made an impression.” Mr. Dzhakishev added that Kazatomprom chose to form a partnership with Mr. Giustra’s company based solely on the merits of its offer.

After The Times told Mr. Giustra that others said he had discussed the deal with Mr. Nazarbayev, Mr. Giustra responded that he “may well have mentioned my general interest in the Kazakhstan mining business to him, but I did not discuss the ongoing” efforts.

As Mrs. Clinton’s presidential campaign has intensified, Mr. Clinton has begun severing financial ties with Ronald W. Burkle, the supermarket magnate, and Vinod Gupta, the chairman of InfoUSA, to avoid any conflicts of interest. Those two men have harnessed the former president’s clout to expand their businesses while making the Clintons rich through partnership and consulting arrangements.

Mr. Clinton has vowed to continue raising money for his foundation if Mrs. Clinton is elected president, maintaining his connections with a wide network of philanthropic partners.

Mr. Giustra said that while his friendship with the former president “may have elevated my profile in the news media, it has not directly affected any of my business transactions.”

Mining colleagues and analysts agree it has not hurt. Neil MacDonald, the chief executive of a Canadian merchant bank that specializes in mining deals, said Mr. Giustra’s financial success was partly due to a “fantastic network” crowned by Mr. Clinton. “That’s a very solid relationship for him,” Mr. MacDonald said. “I’m sure it’s very much a two-way relationship because that’s the way Frank operates.”