There is a material risk the United States would lose its triple-A if there is a repeat of 2011 wrangling over raising the country's self-imposed debt ceiling, rating firm Fitch said on Tuesday.

"If anything the pressure on the U.S. rating is increasing," Fitch's head of sovereign ratings David Riley said at a conference hosted by the firm.

"If we have a repeat of the August 2011 debt ceiling crisis we will place the U.S. rating under review. There will be a material risk of the U.S. rating coming down," he added.

(Reporting by Marc Jones and Will James)