Police in Egypt have arrested 15 members of the banned opposition Muslim Brotherhood on the eve of a referendum on planned electoral changes.
Protesters have held several rallies against previous arrests of Brotherhood members
They were seized for possessing fliers urging a boycott of the referendum.
More than 800 members of the Muslim Brotherhood have been arrested this month for protesting against the vote.
Opposition groups say the proposals allowing multi-candidate elections contain too many constraints for anyone to challenge President Hosni Mubarak.
In a recorded speech on state television on the eve of the poll, Mr Mubarak said the referendum would be "a decisive moment in our contemporary history".
"I have full and unlimited confidence that you will turn out to take part, through the referendum, in making a new tomorrow for our country and exploring new and broad horizons in our political life," Mr Mubarak said.
The Muslim brotherhood activists were arrested in the provinces of Kafr el-Sheik and Ismailiya.
In the capital, Cairo, police dispersed a small demonstration against the constitutional amendment.
Two members of the opposition al-Ghad party were arrested at the rally where about 20 protesters were surrounded by about 100 policemen.
"What happened today is a proof of a police state, and the authoritarian regime that muzzles mouths and oppresses the opposition," said Ehab al-Khouli, al-Ghad deputy secretary-general, one of the two held.
Under the new proposals political parties have to have been in existence for five years before they can field candidates.
President Mubarak is expected to seek a fifth six-year term
Independent presidential candidates must have the support of at least 65 out of a total of 444 MPs - 90% of whom are from the president's National Democratic Party.
The opposition says a non-government candidate would not get this support - he would depend on the ruling party to back his candidacy.
Under the existing system, voters could only vote yes or no to a single presidential candidate chosen by parliament.
The Muslim Brotherhood - the most popular opposition force in Egypt - is tolerated by the authorities but banned from operating as a political party.
It has 17 MPs sitting in parliament as independents.
On Sunday, police arrested Mahmud Ezzat, Mr Ezzat the Brotherhood's secretary-general. He was believed to have been the highest-profile arrest from the group since 1996.