Policemen and soccer fans argue during a scuffle as fans attempt to enter a stadium to watch a match, on the outskirts of Cairo February 8, 2015. (Al Youm Al Saabi/Reuters)

A riot broke out Sunday night outside a major soccer game in Egypt, with a stampede and fighting between police and fans killing at least 25 people, authorities said.

The riot, only three years after similar violence left 74 people dead, began ahead of a match between Egyptian Premier League clubs Zamalek and ENPPI at the Air Defense Stadium east of Cairo. Such attacks in the past have sparked days of violent protests pitting the country’s hard-core fans against police officers in a nation already on edge after years of revolt and turmoil.

A statement from Egypt’s public prosecutor said that 25 people had been killed and that an investigation had been ordered.

The cause of the violence wasn’t immediately clear. Security officials said Zamalek fans tried to force their way into the match without tickets, sparking clashes. Fans have only recently been allowed back at matches, and the Interior Ministry planned to let only 10,000 fans into the stadium, which has a capacity of about 30,000, the officials said.

Zamalek fans, known as “White Knights,” posted on their group’s official Facebook page that the violence began because authorities opened just one narrow, barbed-wire door to let them in. They said that led to pushing and shoving that later prompted police officers to fire tear-gas and birdshot.

Soccer fans hold lit flares in the stands as they watch a match between Egyptian Premier League clubs Zamalek and ENPPI at Air Defense Stadium in a suburb east of Cairo, Egypt, Sunday, Feb. 8, 2015. (Ahmed Abd El-Gwad/AP)

A fan who tried to attend the game, who spoke to the Associated Press on the condition of anonymity for fear of being targeted by police, said that the stampede was caused by police who fired tear-gas at the tightly packed crowd.

“Those who fell down could not get back up again,” the man said.

The Zamalek fan group later posted pictures on Facebook it claimed were of dead fans, including the names of 22 people it said had been killed. The Associated Press could not immediately verify the images, nor the casualty count.

Egypt’s hard-core soccer fans, known as Ultras, frequently clash with police inside and outside stadiums. They are deeply politicized and many participated in the country’s 2011 uprising that forced out President Hosni Mubarak. Many consider them one of the most organized movements in Egypt after the Islamist Muslim Brotherhood, which the government later outlawed as a terrorist organization following the 2013 military overthrow of President Mohamed Morsi, an Islamist.

— Associated Press