Many US politicians had been cautious in their response to the revolt against Mubarak, urging him to be responsive to protesters but in many cases stopping short of calling for him to leave.

But shortly after the nationally televised announcement by the now-former Vice President Omar Suleiman Friday, top American officials voiced their satisfaction at Mubarak's decision to step down and urged all sides in Egypt's rapidly unfolding political drama to ensure a peaceful transition to democracy after their 18-day uprising.

Vice President Joe Biden called the developments in Cairo: “a pivotal moment in history,” saying Friday was a day of “historic” and “dramatic” change, after which the future of Egypt — a critical US ally in the Middle East — will be determined by its people.

The US government will continue to insist on a “set of core principles” in the months ahead, the vice president told an audience in Kentucky. Violence and intimidation against protesters remains unacceptable, he said. The universal rights of people “must be respected” and their “aspirations met.”

Finally, he said, the transition must be “irreversible” and part of a negotiated path to democracy.

President Barack Obama was in a meeting in the Oval Office when he learned that Mubarak was stepping down, said Tommy Vietor, a spokesman for the National Security Council, adding that the president watched television coverage of the events in Egypt for several minutes afterward.

Obama did not talk to Mubarak or Egyptian Vice President Omar Suleiman before the announcement of Mubarak's resignation, said White House Press Secretary Robert Gibbs.

The President was scheduled to speak at 1:30 p.m. Friday, but delayed his speech by several hours.  White House officials said he decided to speak to the leaders in the region before speaking to the nation.

As jubilation spread through the streets of Cairo, Capitol Hill and the White House tried to keep up with fast-paced developments. Shortly before noon here, Egypt's ambassador to the US, Sameh Shoukry, was called to a meeting at the White House, his secretary said.

In Vermont, Sen. Patrick Leahy (D-Vermont) planned an impromptu press conference to respond with ecouragment to Mubarak's departure.

Sen. Bill Nelson, D, Florida, said that Mubarak had “rightly honored the Egyptian people's calls for freedom.” He said that “all nations must now support an orderly, peaceful transition to democracy,” and added that “we hope the first steps of the new government will be to guarantee free and fair elections as soon as possible, while also keeping the peace with all of Egypt's neighbors including Israel.”

Senate Majority Leader Harry Reid, D-Nevada, also issued a statement urging a peaceful transition.

“I am pleased that President Mubarak has heard and heeded the voice of the Egyptian people, who have called for change,” Reid said. But “it is crucial that Mubarak's departure be an orderly one and that it leads to true democracy for Egypt, including free, fair and open elections."

He added, "We caution all sides against violence during this transition.”

Senate Foreign Relations Committee Chairman John Kerry, D-Massachusetts, released a statement calling Mubarak's resignation “an extraordinary moment for Egypt.”

But “what happens next will have repercussions far beyond Egypt's borders,” he said. “We know from recent experience in Gaza that this requires not just elections, but hard work to build a government that is transparent, accountable, and broadly representative.”

US defense officials said they were not given any advance warning of Mubarak's resignation and were not sure it would happen.

The United Nations' Secretary-General, Ban Ki-moon, said he is ready to do all in his power to help Egypt make a peaceful transition to democracy.
 

Conservatives concerned that extremist factions were behind Egypt’s revolution were shrugged off. “This doesn’t have the fingerprints of anyone on it, except those in Tahrir Square,” said Michael Singh, former director for Iran at the National Security Council.

“In the US, there is an irrational fear amongst conservatives in the US that Egypt’s move toward democracy will be hijacked by the Muslim Brotherhood or another group that might prove unfriendly to American interests,” said Amr Hamzawy, at the Washington-based Carnagie Endowment for International Peace.

“But from the very beginning, the uprising across Egypt has been democratic, not ideological. There is no real danger that the revolution will be just the opening that Islamists need to take control,” said Hamzawy.??The next steps in Egypt will be closely watched by US lawmakers, who each year provide about $1.3 billion in aid to Egypt and see the country as essential to a stable Middle East.

The news of Mubarak’s departure was met with a favorable reaction from Wall Street. The Dow, NASDAQ and S&P 500 all saw modest gains.

Just 10 days ago, the unrest is Egypt had a negative effect on global markets: Oil prices spiked, food prices rose and stocks declined.