About 100 people have taken part in a rare anti-government demonstration in the Egyptian capital, Cairo, demanding free elections for the presidency.
'Enough': The protesters are calling for an end to Mubarak's rule
Reports say thousands of policemen were deployed near the Cairo international book fair, where the protest occurred.
Protesters carried placards calling for an end to the rule of President Hosni Mubarak, who may run for a sixth term.
In a related development, Human Rights Watch has called on Egypt to release a number of recent detainees.
The US-based group says the detentions result from what it describes as politically motivated charges.
In a letter to Mr Mubarak, Human Rights Watch called on the government to end the harassment of peaceful dissidents who exercise their rights of freedom of speech and assembly and association.
Recent arrests include Ayman Nour, member of parliament, journalist, and lawyer. Mr Nour leads the reformist al-Ghad, or Tomorrow, party.
A student and nine members of the banned, but often tolerated, Muslim Brotherhood have been detained recently.
Egyptian police also prevented a public appearance by Mohammed al-Said, deputy director of the al-Ahram Centre for Political and Strategic Studies, after he publicly called for constitutional reform.
The Human Rights Watch statement follows US President George W Bush's call for democratic reforms in Egypt, and Saudi Arabia, in his State of the Union address.
The protesters near the Cairo book fair held banners reading "Enough".
The slogan is a reference to the 24 years of uninterrupted rule by Mr Mubarak.
A recent protests called for the release of reformist Ayman Nour
Under the current system, the Egyptian parliament selects one candidate for the presidency.
This candidate then stands in a national referendum.
Protesters also denounced suggestions that the governing National Democratic Party might groom President Mubarak's son Gamal to take over from his father.
The demonstration was organised by the Egyptian Movement for Change, an umbrella group which wants the constitution changed to allow more than one candidate to run for president.