Tear gas rises as protesters clash again with riot police near Cairo's Tahrir Square, and opponents of President Mohamed Mursi rally for a day of mass action.

Many in the country are angry following a decree by President Mursi last week that prevents legal challenges to any decision he makes until a new parliament is elected.

The opposition, accusing Mursi of appointing himself a modern-day Pharaoh, is pressing ahead with Tuesday's protest to demand the scrapping of the decree.

Demonstrators have camped out in Tahrir Square since the decision was announced last week, and violence has flared repeatedly.

Tuesday saw fighting gathering momentum on side streets near Tahrir Square as police fired tear gas at protesters, and stones were thrown in response.