Taliban spokesman on Saturday said Umar had not sent any such letter to Obama.
Earlier media reports quoting former and current US officials said Omar wrote to President Barack Obama last year indicating an interest in talks key to ending the war in Afghanistan.
According to the reports, the previously undisclosed communication was considered authentic by people who saw it, but skeptical administration officials say they cannot determine if it actually came from Omar. The unsigned letter was passed through a Taliban intermediary in July. An administration official says it represented views consistent with what Taliban emissaries had been telling U.S. officials.
Media reports also said a direct message from Omar could be a strong signal that the Taliban movement is interested in negotiation at the highest levels.