Thousands of Greeks took part in demonstrations Sunday to mark the anniversary of a 1973 anti-junta uprising, with police bracing for trouble after a series of raids on anarchists.

This year the protest was heavily influenced by opposition to the new conservative government of Kyriakos Mitsotakis, elected in July on a pledge to strengthen law and order.

The annual demonstation marking the 1973 student uprising against Greece's US-backed military dictatorship regularly descends into violence
The annual demonstation marking the 1973 student uprising against Greece's US-backed military dictatorship regularly descends into violence AFP / ARIS MESSINIS

"Down with the right-wing government" read a banner carried by the protesters. "Uprisings do not end up in museums," some of them chanted.

They also shouted slogans against US President Donald Trump and Turkish President Recep Tayyip Erdogan, and burned EU and US flags.

Some 20,000 people marched in Athens, police said, in remembrance of dozens of people who died in the 1973 military crackdown on a student uprising at the Athens Polytechnic.

The annual anti-junta demonstration in Athens is a treasured anniversary for many Greeks, with over 10,000 people taking part last year
The annual anti-junta demonstration in Athens is a treasured anniversary for many Greeks, with over 10,000 people taking part last year AFP / ARIS MESSINIS

Some 9,000 people demonstrated in Thessaloniki, authorities said. Separate demonstrations were being held in Greece's other major cities.

The annual march in Athens regularly descends into violence and some 5,000 officers were mobilised there for the day, backed by drones, a helicopter and water cannon, police said.

Several youths were arrested after Molotov firebombs and stones were found on a roof in the bohemian district of Exarchia, in an apparent plan to ambush riot police passing below.

This year's anti-junta protest looks set to be dominated by opposition to the new conservative government of Kyriakos Mitsotakis
This year's anti-junta protest looks set to be dominated by opposition to the new conservative government of Kyriakos Mitsotakis AFP / LOUISA GOULIAMAKI

On Wednesday, in a move seen as directed against the demonstration, the government secured parliamentary approval of a law applying harsher penalties for public violence.

Throwing a Molotov cocktail -- a fairly frequent occurrence at demonstrations in Greece -- is now punishable by up to 10 years in prison, instead of five years previously.

Some 5,000 police officers were mobilised in Athens for the day
Some 5,000 police officers were mobilised in Athens for the day AFP / LOUISA GOULIAMAKI

The demonstration marks the 46th anniversary of the student uprising. Traditionally, it ends in front of the American embassy, which was ringed with police vans, as the fervently anti-Communist dictators enjoyed backing from Washington.

At least 24 people were killed in the crackdown, an event generally considered to have broken the junta's grip on power and helped the restoration of democracy.

The bloodstained flag that flew over the Polytechnic's iron gate is traditionally carried at the head of the demonstration in the capital
The bloodstained flag that flew over the Polytechnic's iron gate is traditionally carried at the head of the demonstration in the capital AFP / Louisa GOULIAMAKI

The bloodstained flag that flew over the Polytechnic's iron gate, which was crushed by a tank that night, was carried at the head of the demonstration in the capital, a longstanding tradition.

Athens mayor Kostas Bakoyannis urged respect for the city.

"On this anniversary, let's send out the right message. A shared message about memory," he wrote in a Facebook message Friday.

"We should not obscure the essence which is the struggle of youth for democracy. On this anniversary, let's show respect toward the city."

The anti-junta demonstration is a treasured anniversary for many Greeks.

In recent years, demonstrators have used the anniversary to voice opposition to US "imperialism", and the harsh austerity measures imposed on Greece by international creditors after the global financial crisis.

Mitsotakis's administration has come under fire over a flurry of police operations against anarchist squats and demonstrators.

Main opposition leader Alexis Tsipras, the former PM, on Sunday accused the conservative government of harbouring "junta applauders" in its midst, referring to former far-right politicians given cabinet posts by Mitsotakis.

There is also tension over a recent amendment to facilitate police checks in universities, which has prompted several student protests.

"Police have no place in universities... but neither does lawlessness," Citizen's Protection Minister Michalis Chrysohoidis told To Vima weekly on Sunday.

This week the Polytechnic's rector Andreas Bantouvas said: "We need to be careful these days, and (public) comments must be guarded."

Justice Minister Kostas Tsiaras, speaking ahead of Wednesday's parliamentary vote, told lawmakers ahead of the vote in parliament: "Laws and regulations are needed for Greek citizens to feel safe."

On Monday, some 200 students demonstrating at the Athens University of Economics were surrounded by anti-riot police who used tear gas and arrested two protesters.