U.S. President Barack Obama on Friday said Egypt would never be the same now that Hosni Mubarak had stepped down as president after 30 years in power, but noted that it was only the beginning of the nation's transition.

"The people of Egypt have spoken," said Obama, speaking from the White House. "Their voices have been heard and Egypt will never be the same," he said. "By stepping down, president Mubarak responded to the Egyptian people's hunger for change."

Obama also said that there were likely to be "many difficult days ahead."

"The military has served patriotically and responsibly as a caretaker of the state and will now have to ensure a transition that is credible in the eyes of the people," Obama said. He said the military must protect the rights of Egyptian citizens, lift the emergency law, revise the constitution and other laws, and lay out a clear path to free and fair elections to make the change "irreversible."

"Above all, this transition must bring all of Egypt's voices to the table," Obama said.

He praised the Egyptian people, particularly its youth, for their peaceful demonstrations and invoked the words of U.S. civil rights leader Martin Luther King Jr. who, in celebrating the post-colonial birth of Ghana, said: 'There's something in the soul that cries out for freedom.'

"Those were the cries from Tahrir Square and the world has taken note," Obama said.

Today, on the 18th day of demonstrations, protesters at Tahrir Square were jubilant, waving flags in the air, setting off fireworks, cheering and shouting after learning that Mubarak had stepped down. They seemed to focus little on the latest statement of the Supreme Council of the Armed Forces, which went on state television to say it was studying the issue of leading the country and would define concrete steps later.

United Nations Secretary-General Ban Ki-Moon called for a "transparent, orderly and peaceful transition" in Egypt and said he wanted to see free and fair elections.