There have been suggestions protesters will try to gather for a second day Egypt protests: Demonstrators 'face prosecution'
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The BBC's Jon Leyne: "Tear gas and water cannon were used against protesters"
Public gatherings, protests and marches will no longer be tolerated, the interior ministry has said.The warning came as a fourth person died after nationwide protests, which were broken up with tear gas overnight.
Medics said the injured person died in Suez, in the east of Egypt, where two protesters were killed on Tuesday.
A police officer was also killed amid the violence in Cairo.
Police used water cannon late on Tuesday as they forced protesters from Tahrir Square, a symbolic city centre location in the heart of Cairo.
Analysis
But this does contrast with a statement from the foreign ministry, which claimed the country had an open environment of freedom of expression. There have been some calls for new demonstrations, but so far no substantial numbers have gathered and even the police presence is not overwhelming.
Protesters had been inspired by the recent uprising in Tunisia, vowing to stay until the government fell.
Small crowds had gathered in Tahrir Square on Wednesday morning, just hours after the last protesters were removed. But there were few signs of a heavy police presence.Demonstrations are illegal in Egypt, which has been ruled by President Hosni Mubarak since 1981. The government tolerates little dissent and opposition demonstrations are routinely outlawed.
In Washington, the White House urged the Egyptian government to allow protests to go ahead, describing the situation as "an important opportunity" for the nation.
France's foreign minister said she regretted the loss of life in Egypt but said democracy should be encouraged in all countries around the world.
Social protesting
Tuesday's event had been co-ordinated on a Facebook page, where the organisers said they were taking a stand against torture, poverty, corruption and unemployment.
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We believe that the open exchange of information and views benefits societies and helps governments connect with their people”
They said that the rally would mark "the beginning of the end".
The BBC's Jon Leyne, in Cairo, said that it had been unclear how many people would respond to the online call, but in the end, the turnout was more than the organisers could have hoped.Police were taken aback by the anger of the crowd and let protesters make their way to Tahrir Square near the parliament building, he says.
Microblogging site Twitter also played a key part, with supporters inside and outside Egypt using the search term #jan25 to post news of the day.
However, Twitter confirmed later on Tuesday that it had been blocked inside Egypt from 1600 GMT, meaning many were unable to post updates from the scene.
"We believe that the open exchange of information and views benefits societies and helps governments connect with their people," Twitter said on its official account.
There have been renewed calls for protest on Wednesday, but there is no indication yet whether they will attract large crowds.
'Mubarak the coward'
The crowd's anger was largely focused on the president on Tuesday, with thousands calling for his resignation and "Down with Mubarak" scrawled on the walls of buildings.
But at 0100 local time (2300 GMT Tuesday) police moved in, firing tear gas and driving protesters into nearby streets. There were reports that some people had been beaten by police.
"It got broken up ugly with everything, shooting, water cannon and [police] running with the sticks," one of the last protesters to leave, Gigi Ibrahim, told the Associated Press.
Protests were also held out in other areas of the country on Tuesday, including the eastern city of Ismailiya.
Thousands joined protests in the northern port city of Alexandria, some chanting: "Revolution, revolution, like a volcano, against Mubarak the coward."
In Washington, the White House said Egypt's government had "an important opportunity to be responsive to the aspirations of the Egyptian people".
In a statement, it said Egypt should "pursue political, economic and social reforms that can improve their lives and help Egypt prosper".
"The United States is committed to working with Egypt and the Egyptian people to advance these goals," it added.
'Rudderless' opposition
The Egyptian government said it had allowed Tuesday's protesters "to voice their demands and exercise their freedom of expression".
It blamed the violence on the banned Islamist movement the Muslim Brotherhood, although they were reported to have been ambivalent about the protests.
One opposition leader, Mohamed ElBaradei, had called on Egyptians to take part in the protests.
Tunisia's President Zine al-Abidine Ben Ali was ousted from power and fled the country earlier this month, after weeks of protests in which dozens of people were killed.
Egypt has many of the same social and political problems that brought about the unrest in Tunisia - rising food prices, high unemployment and anger at official corruption.
However, the population of Egypt has a much lower level of education than Tunisia. Illiteracy is high and internet penetration is low.
There are deep frustrations in Egyptian society, our Cairo correspondent says, adding that Egypt is widely seen to have lost power, status and prestige in the three decades of President Mubarak's rule.
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