Protests commenced on Sunday in support of toppled Islamist president Mohamed Morsi in Cairo and elsewhere, with one fatality, as the country marks the 40th anniversary of the 1973 Arab-Israeli war.
Armoured vehicles and security forces have been heavily deployed within main squares across the nation, as fears heighten of a violent flare-up between the protesters and crowds celebrating the war anniversary.
In the flashpoint Tahrir Square in downtown Cairo, an Ahram reporter said people were queuing to stream into the area to celebrate the national holiday. There is a celebratory atmosphere, but security is evident.
Protesters, many clad in T-shirts bearing the photo of army chief General Abdel Fattah El-Sisi or holding his picture, have converged on the square in their thousands as patriotic songs boom from loud speakers.
People walk through metal detectors and are thoroughly searched by police and army personnel as they enter the square, with only two entrances open. All other routes in are sealed off, according to Ahram Online's Osman El-Sharnoubi.
Egypt's army traditionally celebrates the October war against Israel – which eventually led to the recovery of the Sinai Peninsula – each year with military performances and flyovers, and the day is a public holiday.
The Interior Ministry warned it would "firmly confront" any violence during demonstrations on Sunday.
Backers of Morsi's Muslim Brotherhood have staged thousand-strong marches in several parts of Cairo, Giza and other governorates.
Flexing its muscles, a pro-Morsi Islamist group urged followers to converge on Tahrir Square, the epicentre of the 2011 uprising and 2012 demonstrations against Morsi's rule.
However, police and army troops have barred Islamist marches from reaching the capital's major squares, as army jets and F-16 fighters hover in formations over Cairo, Alexandria and several other cities.
Almost two dozen Islamists were arrested early on Sunday in northeast Cairo while marching towards the Rabaa Al-Adawiya area, which security forces raided in mid-August to disperse a sizeable extended sit-in by Morsi loyalists, leaving hundreds dead.
The area, along with other major squares, has been sealed off to protesters since the police crackdown.
In Cairo's Mohandeseen district, thousands of Morsi backers have been marching through the area, many flashing the four-finger Rabaa sign and chanting anti-army slogans, reported Ahram Online's Sherif Tarek.
The National Alliance to Support Legitimacy, a pro-Morsi grouping led by the Brotherhood movement, has repeatedly called for protests against the military's overthrow of Morsi.
However, its ability to muster large crowds has tailed off as security forces have mounted a crackdown on Islamists, arresting hundreds of members and allies including Morsi himself.
Rallies took a violent turn in central Cairo's Garden City and Giza's Dokki district, where police fired rounds of teargas after local residents clashed during pro-Morsi protests heading towards Tahrir, eyewitnesses and Ahram Online reporters said. The sound of heavy gunfire was later reported.
In Delga - a town south of Cairo held by Islamists until security forces raided it last month - a Brotherhood supporter was killed and at least three injured as a pro-Morsi march clashed with police. Protesters hurled stones at security officers near a police station, and officers responded with live fire.
Six people were injured, including three policemen, in clashes in Suez when security forces fired teargas at a march by pro-Morsi demonstrators, Al-Ahram Arabic news website reported. The confrontation had occured when the march approached a central square where pro-military crowds were celebrating the national holiday.
In Alexandria, clashes broke out between Morsi supporters and residents in Sidi Beshr district after a pro-Morsi march.
Skirmishes also took place in Ismailia, Beheira governorate and in Aswan in the south of the country.
Pro-army demonstrations were reported in Kafr El-Sheikh, Port Said, Sohag, Mahalla, Damietta and other locations.
Egypt has been gripped by prolonged violence since the military overthrow of Morsi early in July after mass demonstrations against his turbulent year in office.
The ouster of the former president enraged Islamists, who have denounced the move as a violation of democratic "legitimacy."
Hundreds were killed on 14 August when security forces moved to forcibly disperse two protest camps set up by Morsi loyalists in Cairo and Giza, unleashing days of violent turmoil and deepening polarisation.
Militants elsewhere have taken up arms against the state.The army has been battling an insurgency in the Sinai Peninsula, adjoining Israel and the Palestinian Gaza Strip, where Islamist militants have mounted almost daily attacks on security and army targets, killing dozens.
