Officials originally said that the statement would take place in the White House press briefing room at 1:30 p.m (1830 GMT) but later said that it would take place in the presidential mansion's Grand Foyer at a time to be decided.

Obama was told of Mubarak's decision to step down and hand power to the military on Friday during a meeting in the Oval Office, National Security Council spokesman Tommy Vietor said.

The president then watched coverage of riotous scenes of celebration from Cairo's Tahrir Square on television.

In a first US reaction to events in Egypt, US Vice President Joe Biden warned of "delicate and fateful" days ahead, and said the ouster of Mubarak was a "pivotal moment" in the Middle East.

Biden said the "dramatic changes" in Egypt must meet the aspirations of massive crowds in Cairo, adding that "the transition taking place must be an irreversible change and a negotiated path towards democracy."

The US vice president made his remarks during a previously scheduled speech at the University of Louisville, Kentucky.