CAIRO, Jan 10 (Reuters) - Three people were killed in clashes in Egypt on Friday, security sources said, ahead of a referendum next week on a new constitution.
Ousted President Mohamed Mursi's Muslim Brotherhood has called for a boycott of the January 14 and 15 referendum, which is also seen by some as a vote on army chief General Abdel Fattah al-Sisi's popularity.
Sisi overthrew Mursi in July following mass protests against his rule and could yet run for president of the Arab world's biggest country.
The Brotherhood says Sisi's overthrow of Mursi constituted a coup which undermined democratic gains made since a 2011 popular uprising toppled autocrat Hosni Mubarak.
The referendum is the first milestone in a political transformation that Sisi has said would lead to presidential and parliamentary elections and bring stability to Egypt, which has a peace treaty with Israel and controls the Suez Canal.
But Islamist militants have stepped up attacks on security forces since Mursi's ouster, and street violence has continued, conditions which have decimated investment and tourism.
On Friday, two people were killed in the city of Suez in clashes between supporters and opponents of Mursi, who is on trial for charges including incitement to murder.
In Egypt's second city of Alexandria, one person was killed in clashes, said security sources.
A crackdown on the Brotherhood has limited its ability to hold street protests it had hoped would bring down the army-backed government.
Hundreds of members have been killed and the group's leaders have been jailed.
(Reporting by Michael Georgy)