A coalition has called for a boycott of Egypt's vote for a new constitution, which some see as an "indictor" of the army chief's presidential bid.
Egyptians vote for a new constitution on Tuesday in a referendum seen as a test of support for a presidential bid by army chief Abdel Fattah al-Sisi, almost seven months after he toppled Mohamed Morsi.
An Islamist coalition led by Morsi's Muslim Brotherhood has called for a boycott and "civilised peaceful protests" during the two-day referendum, but the interior ministry has pledged to "decisively" confront any attempts to disrupt voting.
The military-installed government hopes the vote, the first since Morsi's overthrow in July, will shore up its disputed authority after a brutal crackdown on Morsi's supporters, who have denounced the "sham referendum".
While it is uncertain how many Egyptians will vote amid concern over violence and militant attacks, the constitution appears certain to pass.
It has done away with much of the Islamist-inspired wording of Morsi's constitution, which was suspended on his overthrow, and its supporters say it expands women's rights and freedom of speech.
But it has bolstered the military's powers, granting the army the right to appoint the defence minister for the next eight years and to try civilians for attacks on the armed forces.
Runup to the vote
Interim president Adly Mansour implored Egyptians to turn out at the polls, which will be secured by hundreds of thousands of soldiers and police officers across the country.
"I call on you to live up to the responsibility you owe to your nation and to ensure a better future for this country to go to your polling station and vote," he said in a speech on Sunday.
The runup to the vote has been marred by a deadly crackdown on Morsi's supporters, and arrests of activists who campaigned for a "No" vote.
At least seven activists have been detained in the past week while distributing posters or leaflets critical of the new constitution, prominent rights lawyer Ragia Omran said, adding most were released after a few days.
The capital, meanwhile, has been festooned with banners urging Egyptians to vote "Yes", often featuring military motifs such as a general's hat, an allusion to army chief Abdel Fattah al-Sisi.
Many Islamists revile Sisi as the man who overthrew the country's first freely elected and civilian president, but the general is adored by the millions who took to the streets in July to demand Morsi's resignation.
The army chief is widely expected to run for president, and has said he would stand for election if he felt there was "popular demand", state media reported this week.
Sisi will closely monitor the turnout and result of the referendum as an "indicator" of support for a presidential bid, said an official close to the general.
The authorities are worried that a low turnout would empower their Islamist opponents in Morsi's Brotherhood movement and cast further doubt on their legitimacy, analysts say.
At least 1 000 people, mostly Islamists, have been killed in street clashes and thousands have been imprisoned since Morsi's ouster. His supporters continue protests almost every day. – Sapa-AFP