Cairo (CNN) -- Political tensions flared Wednesday after more than 70 people were killed when fans rushed the field and rioted at a soccer game in Egypt.

It was unclear whether intense sports rivalries or political strife caused the clashes in the northeastern city of Port Said.

But hours after the fighting, protesters in Cairo chanted, "Down with military rule" and "Tomorrow we come, we take the military down." And the secretary-general of the Muslim Brotherhood party blamed Egypt's military for the deaths.

Egypt's interior ministry blamed fans for provoking police.

"There were organized groups in the crowds that purposely provoked the police all through the match and escalated the violence and stormed onto the field after the final whistle," Gen. Marwan Mustapha said. "Our policemen tried to contain them but not engage."

At least 47 people were arrested after the clashes, he said.

The clashes left at least 73 dead and 1,000 people injured, 150 of them critically, health ministry spokesman Dr. Hisham Shiha said. Most of the injured had concussions and deep cuts, he said.

Soccer riot death toll climbs in Egypt

Soccer in the Middle East and security

The fighting occurred in a stadium in the northeastern city of Port Said after the home Al-Masry team beat Cairo's Al-Ahly team 3-1.

Fans from both sides bashed each other with rocks and chairs, said Mohamed Sultan, head of the ambulance association in Port Said.

Many of those who died fell from bleachers inside the stadium, according to Ahmed Saeed, an official from the Port Said governor's office.

"The police stood there watching, and the ambulances arrived late. I carried several dead fans in my arms," said Mamdouh Eid, the executive manager of the Al-Ahly fans committee.

Tension was building throughout the game, Eid said, as Port Said fans threw bottles and rocks at players. Many Al-Ahly fans were trapped in the bleachers during the fighting, he said, because police did not open gates that would have allowed them to exit the stadium.

"Some fell off bleachers, others suffocated, and many were beaten to death and stabbed by knives," Eid said.

When the clashes broke out, about 22,000 people were inside the stadium, which can hold up to 25,000 people. About 2,000 Al-Ahly fans were at the game, he said.

Authorities have been dispatched to hospitals to interview the wounded and investigate, said Adel Saeed, a spokesman for Egypt's general prosecutor.

Egypt's military deployed two planes to transport the Al-Ahly team, some of its fans and some of the injured back to Cairo, he said.

Port Said is about 125 miles (200 km) northeast of Cairo, where hundreds of angry fans gathered outside the Al-Ahly club's headquarters, vowing revenge.

"This is a plot to stir violence in Egypt. Why would a winning team attack others ... and kill them? We will not let this one go," Al-Ahly fan Ahmed Tabaei said.

Protesters outside the club chanted, "Down with military rule; leave it to civilian rule."

The Muslim Brotherhood condemned the violence and said authorities had failed to protect citizens.

"It's a security vacuum in the whole country that has led to armed robberies on banks and random killings. Some have threatened rebellion against the parliament and threatened the youth of the Muslim Brotherhood ... which may indicate that some police officers may be punishing the citizens for causing a revolution," the party said in a statement.

While authorities were responding to the fighting in Port Said, a fire broke out during a match in a Cairo stadium. It was not immediately clear whether the incidents were related.

Lawmakers were scheduled to discuss the situation in an emergency session of Egypt's parliament Thursday.

Sepp Blatter, president of the sport's international governing body, FIFA, said he was "very shocked and saddened" by the events.

"This is a black day for football. Such a catastrophic situation is unimaginable and should not happen," Blatter said in a statement.

The large death toll from the fighting is unprecedented in Egyptian soccer, CNN contributor James Montague said.

"It's not unheard-of to have organized violence between football clubs (in Egypt), but something on this scale has never been seen before," said Montague, who researched soccer in the Middle East for his book "When Friday Comes: Football in the War Zone."

During Egypt's revolution, well-organized groups of soccer fans became a powerful force for political change, he said. Soccer was also closely tied with former Egyptian President Hosni Mubarak's government, which used the sport to boost his popularity, Montague said.

But it was unclear whether political fury fueled Wednesday's clashes.

"There's been a security vacuum, so we don't know whether it's that or whether there's a Mubarak element to it. We just don't know at the moment," Montague said.