CAIRO, Jan 14 (Aswat Masriya) Three Muslim Brotherhood supporters were shot dead and 20 were injured when security forces dispersed a demonstration they organized against the constitutional referendum in Upper Egypt's Sohag on Tuesday, a security source said.

The source explained that when security forces started dispersing the Brotherhood demonstration with teargas, some of the protesters tried attacking the forces. 

The authorities arrested tens of protesters, including three women.

Egyptians have started voting on a draft constitution in a referendum seen by the interim government as a stepping stone towards democracy, but by Islamists, who will boycott it, as illegitimate.

A 50-member assembly, chaired by politician Amr Moussa, wrote this new constitution to replace another written by an Islamist-led assembly under the Mohamed Mursi administration and suspended by the army in July.

The army ousted Mursi in July in response to mass demonstrations against his rule, suspended his constitution and called for early parliamentary and presidential elections.

Egypt’s army has promised intense security of the two-day voting process, in cooperation with the police.

Parliamentary and presidential elections are expected to kick off after the referendum, but in which order they will be conducted is yet to be decided.

Egyptians living abroad finished casting their votes on January 12.