"We have put a series of real choices to the government of Egypt, but in the end they have to make those choices," Kerry told reporters, adding it was "a key moment for Egypt. It's really a tipping point for Egypt."

Kerry, who visited Cairo in March unlocking some $250 million in US aid to help revive the economy, admitted President Barack Obama and the administration "share real concerns about the direction that Egypt appears to be moving in."

"It is our hope that there is still time to be able to turn a corner," he said after talks with South Korean Foreign Minister Yun Byung-se.

"But the recent arrests, the violence in the streets, the lack of inclusivity with respect to the opposition in public ways that make a difference to the people of Egypt, are all of concern today."

There has been increasing concern in the West about a number of legal complaints against journalists, which have cast doubt on President Mohamed Morsi's commitment to freedom of expression.

Greater press freedom was also one of the key demands of the popular uprising that toppled long-time leader Hosni Mubarak in 2011.

Egypt's prosecution on Tuesday was probing complaints of "threatening public security" against a popular satirist, Bassem Youssef, who is already on bail facing charges of insulting the president and offending Islam.

Human rights lawyers say there have been four times as many lawsuits for insulting the president under Morsi than during the entire 30 years of Mubarak's rule.

Kerry said the United States had been working very hard with the Egyptian government in past weeks to get it to reach out to the opposition and to seal a deal with the IMF on a long-mooted loan which could reach $4.8 billion.

The International Monetary Fund is expected to hold further talks with Cairo this week, and has said it could provide an emergency short-term loan to Egypt if needed, as talks on the longer-term financing program drag on.

But the global crisis lender said Cairo would have to show its commitment to reform even to receive a loan from its Rapid Financing Instrument program.

Kerry stressed Washington was not trying to support one party over another, but wanted "to help the people of Egypt to realize the dreams that they expressed in Tahrir Square" and their yearning for democracy.