CAIRO, Egypt -- Rival crowds of supporters of Egypt's military and backers of the Islamist president deposed by the army poured into streets around the country Sunday, as a holiday marking the anniversary of the last war with Israel turned into a showdown between the country's two camps.

Several thousand supporters of the military rallied in Cairo's central Tahrir Square, waving Egyptian flags, blowing whistles and touting posters of army chief Gen. Abdel-Fattah el-Sissi, who ousted President Mohammed Morsi three months ago. In a festive atmosphere, a military band in green jackets and off white pants played, and men spun in whirling dervish-style dances.

At the same time, thousands of Islamist backers of Morsi held marches around the city, shouting slogans against el-Sissi as some headed toward Tahrir Square in hopes of forcing their way into the sprawling plaza. That raised the possibility of violent clashes between the two sides.

Police fired into the air and lobbed tear gas to push back several pro-Morsi marches as they neared Tahrir. Soldiers barricaded entrances to the square with barbed wire and armoured personnel vehicles. Metal detectors were installed at the entrances and demonstrators pouring into the square were searched by troops.

"The people have one demand: Remove el-Sissi and the president," Islamist protesters chanted, referring to the interim president installed after Morsi's fall.

Violence quickly erupted in southern Egypt, where one Morsi supporter was killed in the town of Dalga. Police opened fire on a march by Islamists after some of the protesters fired birdshot at the police, according to the provincial security chief, Osama Metwali.

Dalga, in southern Minya province, is an Islamist stronghold that security forces raided last month to uproot militants who had driven out local police. Farther south in Assiut province, another bastion of Islamic militancy, police fired tear gas to disperse pro-Morsi protests and arrested seven demonstrators, including three women, according to local security chief Aboul-Qassim Abou-Deif.

In the Red Sea city of Suez, security officials said 12 people were injured in clashes between Morsi's supporters and residents who back the military. In the Mediterranean port city of Alexandria, police detained 35 Morsi supporters.

Sunday is the 40th anniversary of Egypt's opening strike against Israel in the 1973 Mideast war, a day celebrated every year here as a victory over Israel, though the war itself ended in a stalemate.

Now it has become mired in Egypt's political turmoil. Three months after Morsi's ouster in a July 3 coup, his Muslim Brotherhood and its Islamist allies are aiming to show their cause remains alive despite a crackdown that has crushed its leadership.

For the military-backed government that replaced Morsi's administration, the day was an opportunity to stoke the pro-army fervour that has pervaded the country since the coup. The army ousted Morsi after massive demonstrations demanding his removal, and since his fall, authorities have fanned the nationalist spirit in part to counter the Brotherhood's persistent protests.

That spirit was in evidence in Tahrir, where some of the demonstrators used the occasion to campaign for el-Sissi to contest the presidential election slated for early 2014. They distributed a petition calling for el-Sissi to run.

"If el-Sissi runs he will definitely win," said Omar el-Shal, a demonstrator in Tahrir. "I will support him if he runs because all other political figures faded away after he came onto the political scene."

Morsi was Egypt's first civilian president, following four with military backgrounds whose combined 60 years in power stretch back to the early 1950s.

In what was a strikingly different 39th anniversary celebration of the war last year, the Brotherhood had packed Cairo's main stadium with its supporters. Beaming and victoriously waving to the crowd, Morsi entered the stadium riding an open SUV, taking a lap around the track without any of the army's commanders alongside him.

Interim President Adly Mansour gave a nationally televised speech Saturday night urged people to take to the streets to celebrate the Oct. 6 anniversary and "support your army." His media adviser, Ahmed el-Muslemani, said anyone demonstrating against the military during the holiday was doing the work of foreign "agents."

Ushering in the commemoration of the war, some two dozen F-16 jet-fighters staged a celebratory flight over Cairo, a city of 18 million whose streets were uncharacteristically empty by early afternoon even though Oct. 6 has traditionally been a national holiday. Only the scream of the jets broke the quiet.

Tahrir Square is the birthplace of the 2011 uprising against autocrat Hosni Mubarak and has since been the site of choice for Egyptian demonstrators. The possibility of bloodshed there on an occasion revered by most Egyptians is the latest evidence of a destructive schism that began to surface soon after Morsi's narrow election victory in June 2012.

Morsi was ousted in a July 3 coup that followed demonstrations by millions of Egyptians demanding that he step down. Egypt's first freely elected president, Morsi has since been detained in an undisclosed location, something that his supporters refer to as a "kidnapping."

Sunday's faceoff will be the latest episode in the turmoil roiling Egypt since Mubarak's ouster in February 2011. The military-backed government has since Morsi's departure rounded up at least 2,000 members of his Muslim Brotherhood, including most of the Islamist group's leaders. A crackdown on sit-in protest camps by Morsi's supporters and subsequent violence left at least 1,000 people dead.

Brotherhood supporters have since been staging near daily protests to demand Morsi's reinstatement. Their numbers have greatly dwindled in recent weeks but they have been energetically mobilizing for Sunday's rallies, saying they want to celebrate the war's anniversary while denouncing the military leadership that toppled Morsi, Egypt's first freely elected president.

The Brotherhood claims that its protests are peaceful, but there have over the past three months been cases when Morsi's supporters have carried and used firearms, clubs or firebombs.

Liberal politician Khaled Dawoud was attacked by a mob of Morsi supporters this weekend when he was inadvertently caught up in a protest. He said he tried to drive away from the scene but heavy traffic allowed his pursuers to catch up and break his car's windows with rocks.

Dawoud said they stabbed him several times, including once near his heart, and attempted to saw off his left hand. Dawoud, who is the spokesman for the liberal al-Dustour party led by reform leader Mohamed ElBaradei, remains hospitalized.

Dawoud relentlessly campaigned against Morsi's rule but has also criticized the violent crackdown against the Brotherhood and the media's vilification of the group.

It is rare for a figure as prominent as Dawoud to be caught up directly in the widespread political violence. Apart from the bloodshed, the deep political divisions among Egyptians are manifested in a multitude of ways every day as supporters of the military seek to ostracize Brotherhood members in government departments, the education system and trade unions, with heated arguments and fist fights now commonplace.

Associated Press reporter Mariam Rizk contributed to this report.