The thudding discharge of tear-gas cannons and the crackle of gunfire echoed through the streets of Cairo on Sunday as renewed clashes broke out between anti-coup protesters and Egyptian security forces on a national holiday fraught with historical symbolism.

At least 51 people were killed and more than 200 were injured, according to the state-run Middle East News Agency.

Sunday was the deadliest day in Egypt since security forces moved swiftly in August to stamp out the remains of an anti-coup protest movement, after the violent breakup of the Muslim Brotherhood’s protest camps. The Brotherhood-led Anti-­Coup Alliance called on its followers Sunday to take to the streets again Tuesday and Friday.

Egypt’s renewed violence underscored the potential for further unrest in the months ahead, even as the country’s new ­military-backed government wages what rights activists and political analysts have called the most serious crackdown on ­voices of opposition in the country’s recent memory.

Egypt’s interior ministry said Sunday that it had detained more than 400 people in the day’s violence. But anti-coup activists said the bloodshed had only emboldened them in a strategy of continued protest that has changed little since Mohamed Morsi’s July 3 ouster as Egypt’s president.

“Closing roads, blocking entries to public squares and stopping trains and metro lines will never prevent the world from seeing the truth,” the Anti-Coup Alliance said in a statement Sunday night. The group held the state accountable for the deaths and vowed that it would “pursue and prosecute” those responsible. “God save the honorable people of Egypt,” the statement said.

Oct. 6 marked the 40th anniversary of Egypt’s surprise attack against Israeli forces at the Suez Canal in 1973. The victory, which forced a dramatic Israeli retreat, was short-lived, and the Egyptians were later repelled.

But successive military regimes in Egypt have celebrated Oct. 6 as a point of national pride, often using annual victory celebrations to bolster their own support.

A spokesman for Egypt’s presidency said Saturday that anyone protesting the military on Oct. 6 would be considered a foreign agent.

And on Sunday, supporters of the military coup that ousted the country’s first Islamist president used the holiday to draw new comparisons of victory and defeat, heroic leadership and the decades-old dichotomy of Egypt’s victorious military vs. its Islamist rivals.

For many of the military’s supporters, Sunday was as much, if not more, of a celebration of Egypt’s military chief, Gen. Abdel Fatah al-Sissi, who engineered the coup that ousted Morsi and who many here hope will run for president.

“Today is considered his holiday,” said a vendor selling an array of posters bearing Sissi’s face juxtaposed against humiliating depictions of Morsi and his allies in the Muslim Brotherhood. One poster bore an illustration of Sissi as a butcher, slaughtering a sheep with Morsi’s face.

But as the military and its supporters celebrated in the capital’s Tahrir Square with patriotic dance and musical performances, thousands of anti-coup protesters struggled but failed to bring their own rival chants to the iconic space, repelled by swarms of police, tear gas and gunfire.

The rival protests and outbreak of violence highlighted the lingering thrust of an Islamist opposition movement that the country’s interim military-led government has worked hard during the past two months to crush.

Rights activists say that more than a thousand Morsi supporters have been killed and many more arrested since August, effectively decapitating Egypt’s oldest Islamist group, the Muslim Brotherhood, in what human rights groups have called the deadliest political crackdown in Egypt in decades.

Remaining Muslim Brotherhood supporters and anti-coup activists have continued to stage small protests in recent weeks, and many carried yellow posters bearing the four-fingered hand that has become the symbol of their former protest camp outside the Rabaa al-Adawiya mosque in Cairo, where security forces killed more than 600 people in raids on the pro-Morsi camp at Rabaa — which means “four” — and another protest camp on Aug. 14.

Periodically on Sunday, fighter jets roared low overhead in a show of force cheered by the coup’s supporters and jeered by its opponents.

“They want to send a message that they are in control, to intimidate us,” said Manal Mokhtar, a dentist who had joined the anti-coup protest with other female friends and family. “But that will only make us more determined.”

Outside Tahrir, crowds of pro-military Egyptians queued for a quarter of a mile to enter a square tightly cordoned by army vehicles, and where victory ­rhetoric in chants and posters blended support for Sissi with pride in the nation’s military past.

Members of an unofficial Sissi campaign group said they hoped to use the day to lobby the military leader to run for president.

“I’m here to celebrate, but also to support Gen. Sissi,” said Aya Gamal, who had come with her fiance from the port city of Suez.

She clutched a picture of Sissi, alongside two previous Egyptian military leaders — Gamal Abdel Nasser, who presided over the 1952 overthrow of Egypt’s monarchy and an early crackdown on the Brotherhood, and Anwar Sadat, who presided over the 1973 war and the peace treaty five years later between ­Egypt and Israel. Sadat was assassinated by Islamists at his own Oct. 6 celebration.

“Abdel Nasser said it before: ‘You can’t trust the Muslim Brotherhood,’ ” chanted a man among the revelers, as patriotic tunes played.

“This poster has all of Egypt’s greatest leaders on it,” Gamal said.

The protesters across the river who oppose the coup against Morsi “are not Egyptians,” she added, echoing a statement by a government spokesman Saturday. “They should be executed,” she said.

Nihad al-Kilani, a journalist and an anti-coup protester, offered her own narrative. “They want to steal the glory of the 6th of October victory and cloak themselves in it because they have nothing else,” she said.

Lara El Gibaly in Cairo contributed to this report.