Several hundred demonstrators, mostly young men, clashed with police in the streets off Tahrir Square in central Cairo as night fell on Saturday.
The square, which was the focal point of the uprising in early 2011 that overthrew the Mubarak regime, has seen the ebb and flow of demonstrators over the last five days.
Initially they were out to mark the anniversary of week-long violence that saw some 42 die and to demand the security forces be held accountable.
However, fresh anger erupted following a decree made by President Mohamed Morsi on Thursday extending his powers and shielding him from judicial challenge.
Police on Saturday used tear gas to disperse crowds in Tahrir Square, where tens of thousands gathered the day before with some of the demonstrators remaining overnight. Al Arabiya television said Morsi supporters attempted to storm the headquarters of the judiciary in Cairo and clashed with opposition protesters there.
Sporadic cat and mouse spats with police continued after dark on Qasr El Aini Street and Mohamed Mahmoud Street, the sight of last years fatal clashes.
Some of those throwing rocks at police appeared to be as young as 12 years old.
Groups critical of the government have been united by the presidential decree, many arguing that it echoes the autocratic rule of Mubarak and sells out the revolution.
The Muslim Brotherhood, who propelled Morsi to power in June's election, have called for a mass demonstration in Cairo on Tuesday to show support for the president.
Parties opposed to the decree have also called for a protest on Tuesday in Tahrir Square, less than a kilometer from the Brotherhood gathering.
Egyptian opposition: No dialogue with Morsi
Prominent opposition leader Mohamed ElBaradei said on
Saturday there could be no dialogue with Egypt's president until he rescinded a
"dictatorial" decree that he said gave Morsi the
powers of a pharaoh.
Judges, angry at measures seen as undermining
the judiciary, have threatened to strike if the declaration was not revoked and
the opposition has called for more protests.
"There is no room for dialogue when a dictator imposes the most
oppressive, abhorrent measures and then says 'let us split the difference',"
ElBaradei said in an interview with Reuters and The Associated Press after talks
with opposition figures.
ElBaradei, who said he expected to be
coordinator of a new opposition National Salvation Front, said Morsi's
declaration threatened Egypt's troubled transition to democracy and actions were
needed to stop a "cycle of violence".
"How are we going to do that? I do
not see any other way other than through Mr. Morsi rescinding his dictatorial
declaration," he said, adding the decree created a "new pharaoh."
/>
In his
decree, Morsi put all his decisions beyond legal challenge as long as there is
no parliament, sacked the unpopular general prosecutor and opened the door to
retrials for the already jailed ousted president Hosni Mubarak and his
aides.
"I am waiting to see, I hope soon, a very strong statement of
condemnation by the US, by Europe and by everybody who really cares about
human dignity," ElBaradei said, speaking from his villa on the outskirts of
Cairo.
Bloomberg contributed to this report