Fresh protests over living conditions and an autocratic government have broken out in Cairo a day after large and deadly demonstrations, calling for the ouster of president Hosni Mubarak, swept across the country.
More than 500 protesters were arrested by security forces as the government vowed to crackdown on them.
On Wednesday evening, thousands of demonstrators were spread throughout downtown Cairo after being dispersed by security forces. Many had gathered on Gelaa Street, near central Tahrir Square - the site of a violent early morning confrontation between security forces and protesters who had been planning to sleep the night in defiance of the government.
Police fired tear gas and broke up concrete to use as rocks to throw at protesters and "egg them on," Al Jazeera's Adam Makary reported.
Protesters lit a fire - possibly on a tyre - in the middle of a nearby street and were pelting police officers with stones, said Al Jazeera correspondent Rawya Rageh.
Meanwhile, prime minister Ahmed Nazif made what may have been the government's first concession to protesters. In a statement to a state news agency, he pledged that the country's leadership was committed to allowing freedom of expression "by legitimate means."
But his statement came as the interior ministry said that 500 protesters had been arrested on Tuesday and Wednesday in an effort to clamp down on the public unrest. The ministry had said earlier on Wednesday that new demonstrations would not be allowed.
Thousands of armoured police had been deployed at key locations around the capital in anticipation of renewed demonstrations on Wednesday, which some have called the most significant in Egypt since massive riots over the price of bread in the 1970s.
Three protesters died in the port city of Suez, east of Cairo, during Tuesday's unrest, and a policeman was also killed when he was hit in the head with a rock in Cairo, an interior ministry official said.
Rageh, reporting from the Egyptian capital on Wednesday, said that the interior ministry had issued a statement banning further protests and threatening anyone encouraging them with investigation.
Dozens of protesters who took part in Tuesday's demonstrations were rounded up and taken in for questioning, Rageh reported, with some potentially facing prosecution.
Al Jazeera's Makary said that over 200 people had gathered to protest before the Lawyers Syndicate, generally perceived as a "safe haven" for demonstrations, since the security forces do not usually interrupt gatherings there.
"The numbers are swelling," Makary said, adding that there were rumours of demonstrators possibly breaking away from the cordon and protesting on the streets. "We don't know what the response to this will be," Makary said.
The interior ministry said that police were forced to respond on Tuesday to protesters who threw rocks and vandalised property, including setting a police car on fire.
The ministry claimed that 18 officers and 85 other members of the force had been injured during the clashes. Security officials also said that 250 protesters had been wounded and another 200 arrested.
Though activists said the number of protesters across the country may have reached into the hundreds of thousands, the ministry said the largest gathering in central Cairo consisted of around 10,000 people and shrunk to around 5,000 by night.
The government officially blamed the Muslim Brotherhood, Egypt's technically banned but largest opposition movement, for fomenting the protests.
But the group said that it would not officially participate in the January 25 protests and denied the accusation.
With just eight months to go before a presidential election that could see the ailing Mubarak run for re-election or attempt to hand power to a successor, protesters in Egypt demanded a solution to the country's grinding poverty and called for "the tyrant" to leave.
"Down with Hosni Mubarak, down with the tyrant," chanted the crowds. "We don't want you!"
The Tunisia link
Protesters explicitly linked their demonstrations to Tunisia's popular uprising, which brought down the 23-year government of Zine El Abidine Ben Ali.
Al Jazeera's Rageh said state-run newspapers downplayed the events in their Wednesday editions, but that opposition and independent papers ran comparatively unbiased headlines.
The independent Al-Masry Al-Youm (Egypt Today) newspaper ran a blunt headline: "A Warning."
The interior ministry, which controls the security forces, said authorities wanted to let the protesters express their opinions and accused the crowds of "insisting on provocation."
"Some threw rocks at police ... and others carried out acts of rioting and damage to state institutions," the ministry said in a statement.
"Egyptians have the right to express themselves," Hosam Zaki, a spokesman for the foreign ministry, said.
The US, a close ally of Egypt that has for years given the country the second-largest amount of foreign aid, called for calm.
"The United States supports the fundamental right of expression and assembly for all people," PJ Crowley, the state department spokesman, said in a statement.
"All parties should exercise restraint, and we call on the Egyptian authorities to handle these protests peacefully."
In Washington DC, Hillary Clinton, the secretary of state, said Egypt's government was "stable" and that Egyptians have the right to protest, though she urged all parties to avoid violence.
Discontent with life in Egypt's authoritarian police state has simmered under the surface for years.
"This is the first time I am protesting, but we have been a cowardly nation. We have to finally say no," Ismail Syed, a hotel worker who struggles to live on a salary of $50 a month, told the Associated Press news agency.
Lamia Rayan, 24, said: "We want to see change, just like in Tunisia."
Nearly half of Egypt's 80 million people live under or just above the poverty line, set by the UN at $2 a day.
Also like the Tunisian protests, the calls to rally in Egypt went out on social network sites Facebook and Twitter.
Throughout Tuesday, organisers used Twitter to give minute-by-minute instructions about where to gather in an attempt to outmanoeuvre the police, until the government blocked it in the late afternoon.
Twitter announced that its service had been blocked in Egypt at about 6pm local time on Tuesday (1600 GMT), and said that Twitter and its applications had been affected.
In a message, the company wrote: "We believe that the open exchange of info & views benefits societies & helps governments better connect with their people."
Among the protesters in Cairo was Alaa al-Aswany, author of the best-selling Yacoubian Building, which portrays corrupt politicians, police brutality and terrorism in Egypt.
A keen observer of Egyptian society, al-Aswany said the demonstrations were an important opening for the government's opponents.
"They broke the barrier of fear,'' he said. "The writers of the regime were saying Egypt is not Tunisia and Egyptians are less educated than Tunisians. But here is the thing: these young people proved they can take their rights forcefully."
Mubarak, 82, has not appointed a deputy since he became president in 1981 and is widely thought to be grooming his son Gamal to succeed him.