On the day Egyptians headed to the polls to vote on a controversial referendum, violence broke out in Cairo - at the offices of an opposition party's newspaper.

Sources said Islamist activists targeted the Wafd party using petrol bombs on Saturday. At least two people were reportedly injured.

The attack is the latest in a series of violent incidents surrounding the referendum - on a new constitution - largely written by the allies of President Mohammed Mursi.

Supporters say it would lead to democratic transition - but critics maintain it does not give enough rights to women and minorities.

Because of high voter turnout earlier in the day, polls stayed open late Saturday night.. before officials began counting votes after the polling stations closed.

Official results will not come until after a second round of voting takes place in various parts of the country next Saturday.