ATHENS — Police detained several dozen people and fired tear gas in Athens Tuesday as hundreds of protesters defied a ban on gatherings of more than three people to mark the anniversary of the crushing of a 1973 student uprising against the military junta then ruling Greece.

Nov. 17, the day the uprising was quashed, is marked each year with wreath-laying ceremonies at the Athens Polytechnic commemorating those who died there, followed by marches to the U.S. Embassy. The United States had backed the dictatorship that ruled Greece for seven years from 1967.

But the government banned this year's events, citing public health concerns as the country struggles to contain a resurgence of the coronavirus that is straining hospitals and leading to record numbers of deaths. A nationwide lockdown has been imposed until the end of the month, but authorities tightened restrictions during the Polytechnic anniversary, banning gatherings of four or more people from Nov. 15-18. 

Police officers detain a man during a protest in central Athens, on Tuesday, Nov. 17, 2020. (AP Photo/Thanassis Stavrakis)

Thousands of police were deployed in Athens and the northern city of Thessaloniki to prevent marches. The annual Polytechnic marches often turn violent, with protesters clashing with riot police. 

Left-wing opposition parties decried the ban as unconstitutional, although the country's highest administrative court, the Council of State, ruled otherwise.

Three left-wing parties, including main opposition party Syriza, defied the ban, as did other groups.

A Communist Party-backed union held an initial brief gathering outside the U.S. Embassy Tuesday morning, with about 250 people wearing masks and marching in formation, maintaining distance from one another. 

But a later, larger gathering by about 1,500 people in central Athens dissolved after police detained several people and eventually used tear gas and a water cannon.

Police officers on motorcycles patrol outside the Athens Polytechnic in central Athens, on Tuesday, Nov. 17, 2020. (AP Photo/Thanassis Stavrakis)

In a statement, the Civil Protection Ministry said police had repeatedly requested the protesters disperse, to no avail. 

"Those who, through their actions, show disregard for what is happening around them, are displaying antisocial behavior and contempt for those fighting for their lives in the hospitals," the statement said.

 Authorities said about 100 people in total were detained across Athens.

Police were also detaining protesters defying the ban in the northern city of Thessaloniki. Penalties range from 300 euros for individuals attending a gathering that violates the ban, to 3,000 euros for organizers and 5,000 euros for organizations who arrange the events.

A small group of people also threw firebombs at a police station in Thessaloniki, causing no injuries or damage. 

Riot Police officers walk next to a water cannon vehicle, in central Athens, on Tuesday, Nov. 17, 2020. (AP Photo/Thanassis Stavrakis)

Former prime minister Alexis Tsipras, who heads the main opposition Syriza party, posted a photo of himself attending a socially distanced gathering for the Polytechnic Tuesday.

"With responsibility and observance of health protection measures, this year we again honored the dead and the struggles of our people for democracy, independence, and justice," he said in a post on social media.

A protester resists as police try to detain him during a banned rally in the northern city of Thessaloniki, Greece, Tuesday, Nov. 17, 2020. (AP Photo/Giannis Papanikos)

"We broke the senseless ban," he said. "Democracy and historical memory cannot be quarantined."

Earlier in the day, Prime Minister Kyriakos Mitsotakis laid a wreath at the Athens Polytechnic amid tight security.

"Every important anniversary gains new meaning through the conditions in which it is celebrated," Mitsotakis said, adding that current priorities were protecting public health and showing solidarity with young people affected by the financial crisis. 

The police use a water cannon against protesters from the communist party-affiliated PAME union during clashes in central Athens, on Tuesday, Nov. 17, 2020. (AP Photo/Thanassis Stavrakis)

Greece is under lockdown until Nov. 30 as authorities struggle to contain a coronavirus resurgence that has seen infections spike across the country. On Sunday, Greece recorded its largest coronavirus death toll in a single day: 71. 

The European Union nation of 11 million people now has nearly 79,000 confirmed cases and more than 1,200 deaths, while its intensive care units are quickly reaching capacity. 

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By ELENA BECATOROS Associated Press

Costas Kantouris in Thessaloniki, Greece, and Derek Gatopoulos in Athens contributed to this report.