Egyptian protesters have clashed with police in Cairo for a fourth straight day as they demand an accelerated presidential election and early handover of power from the ruling military council to a civilian government.

Hundreds of riot police guarding Egypt's interior ministry fired tear gas, rubber bullets and birdshot Sunday to keep stone-throwing demonstrators away from the building. Protesters accuse the ministry of failing to prevent a melee and stampede that killed 74 people after a football match in the city of Port Said last week.

Officials say at least 12 people have been killed in the cities of Cairo and Suez and 2,500 others have been hurt since protests broke out Thursday.

Some Egyptians believe remnants of ousted president Hosni Mubarak's government were behind the Port Said violence and see it as part of a plot to create chaos to reassert influence.

A number of Egyptian commentators say plainclothes officers took part in the violence and allege that riot police intentionally allowed the melee in Port Said as a way to retaliate against fans of the visiting team, Al-Ahly, known as Ultras. A network of Ultras played a key role in clashes with security forces during the uprising that toppled Mr. Mubarak last February and now against the military council that took his place in power.

Lawmakers in Egypt's new parliament have blamed police inaction for the Port Said tragedy and voted to conduct an investigation.

The military council's Field Marshal Mohamed Tantawi declared three days of national mourning and vowed to find those responsible. Investigators have arrested 47 suspects for the football match mayhem, while the government fired the board of Egypt's football federation and suspended Port Said's governor and security chiefs.

In another development Sunday, saboteurs attacked a gas pipeline that crosses the Sinai peninsula, the 12th such attack in the year since Mr. Mubarak resigned. The explosion halted exports to neighboring Israel and Jordan.