Update 1:39 p.m. ET: "We are witnessing history unfold," President Barack Obama tells supporters in Michigan.
"America will continue to do everything we can to support an orderly and peaceful transition to democracy in Egypt," he said before moving on to previously scheduled remarks promoting his wireless and broadband initiative.
White House press secretary Robert Gibbs told NBC News that Obama was being careful not to get out ahead of an expected statement by Mubarak.
Updated 1:29 p.m. ET: The White House says Obama is scheduled to speak at 1:30 p.m. ET but may run a few minutes late.
President Barack Obama will make brief remarks on Egypt at the top of his remarks in Marquette, Mich., shortly, White House press secretary Robert Gibbs says.
Obama is in Michigan to promote his wireless broadband initiative.