Mohamed ElBaradei, in Tahrir Square, urges US to take action against Mubarak (VIDEO) (PHOTOS)

Opposition leader Mohamed ElBaradei has called on U.S. President Barack Obama to press Egypt President Hosni Mubarak to give up power, and that failing to take more forceful action would cost the U.S. "whatever is left" of its credibility.

ElBaradei, a leading opposition figure, joined thousands of protesters in Tahrir Square in Cairo on Sunday, in continued demonstrations demanding an end to the 30-year rule of  Mubarak.

Al Jazeera reports that Mohamed ElBaradei told protesters in Tahrir Square:

"You have taken back your rights and what we have begun can not go back. … We have one main demand: the end of the regime and the beginning of a new stage, a new Egypt. … I bow to the people of Egypt in respect. I ask of you patience, change is coming in the next few days."

The Arab broadcaster's Web site has posted several audio reports from its correspondents in the square.

ElBaradei said the response of Mubarak so far to the protests and calls for reform by the United States "doesn't even begin to address people's concerns. Peoples' concerns right now is Mubarak has to go, immediately. The first step, if we need to get out of this mess — and it's total mess, security is not there, it's a total chaos situation right now — first step, he has to go."

On Sunday morning, ElBaradei — speaking on CBS' "Face the Nation" — said this week's uprising against Hosni Mubarak had been "many, many years in the making," and that the only option for his country was for the president to go.

"You can't run a country on repression, detention, torture, lack of economic opportunity for 30 years," said ElBaradei, a Nobel laureate.

"This first thing which will calm the situation is for Mubarak to leave, and leave with some dignity. Otherwise I fear that things will get bloody. And you [the United States] have to stop the life support to the dictator and root for the people."

The former Director General of the International Atomic Energy Agency (IAEA), ElBaradei said that the unrest this week, in which dozens have been killed, should not have been a surprise.

"I have been warning of that for many years; many others have been seeing the painting on the wall. There was a tip point when things exploded," he told Bob Schieffer of CBS.

"If Washington didn't see that coming, then there was something wrong with their perception of what was going on in Egypt."