Tens of thousands of people rallied in cities across Europe at the weekend to protest against Russia's ongoing war in Ukraine, with small vigils taking place in Russia as well despite a crackdown by authorities against such demonstrations.

German trade unions called a protest in Berlin, where sunny weather boosted the turnout. The march led from the city's Alexanderplatz — a large square named after Russian Tsar Alexander I — to a site near the Brandenburg Gate.

Many participants carried flags in the blue and yellow colours of Ukraine, while others bore banners reading "Stop the War" and "Peace and Solidarity for the people in Ukraine".

Norbert Herring, who held up a sign that read "What are you doing to your neighbour?" as the crowds filed past the Russian Embassy, said the images from Ukraine reminded him of the bombing of cities during World War II.

Several participants at the Berlin protest said they were Russians ashamed about what their country was doing.

"We're against this war so we wanted to show our solidarity," said Aleksandra Belozerova, a Russian studying in Germany. "It's the least we can do in this situation."

Her friend, Aliia Biktagirova, held a sign with letters for the Russian phrase for "No War" represented as asterisks to reflect the censorship she said is taking place in Russia concerning the conflict.

A pro-Ukraine protest rally in Berlin, Germany. Photo / Michael Sohn, AP

In Russia, where demonstrations against the war in Ukraine have been typically met with a heavy police response, rights group OVD-Info said more than 668 people had been detained in 36 cities as of late afternoon Moscow time.

There was a heavy police presence at central locations including Manezh Square near the Kremlin, with officers carrying demonstrators away to waiting police vans, in footage posted by Russian media. The number of people protesting nationwide appeared to be far fewer than the last major protests a week ago, when OVD-Info listed more than 5000 people who were detained.

Protests were also staged in Warsaw, London and the German cities of Frankfurt, Hamburg and Stuttgart.

People take part in a protest against the Ukraine conflict in Hamburg, Germany. Photo / Daniel Bockwoldt, dpa via AP

In Rome, Pope Francis decried the "barbarianism" of the killing of children and other defenseless civilians in Ukraine. He told a crowd estimated by the Vatican to number 25,000 people gathered in St. Peter's Square for his customary Sunday noon appearance that the attacks must stop "before cities are reduced to cemeteries".

In Cyprus, dozens of Russian nationals joined Ukrainians in the coastal resort town of Limassol Sunday to protest the war in Ukraine. About 50 Russians converged on Limassol's promenade prior to joining with other protesters to chant slogans such as "Stop the war, stop Putin" and waving blue and white flags they said where the Russian national flag without the red stripe that represented "blood and violence".

A Taiwanese woman wears a Ukraine national flag-patterned mask in protest against the invasion of Russia during a march in Taipei. Photo / Chiang Ying-ying, AP

Protester Evgeniya Shlikava, who has been living and working in Cyprus for five years, told The Associated Press that despite Russian propaganda, Ukraine "didn't deserve this action from our government" and that protesters demand an immediate end to the war "that we don't support".

"I do believe that the person who did the most to make Russia weak and not united is Putin himself," said Shlikava who faulted the Russian president and his supporters for bringing the world's wrath on Russia that is proud of its humanistic values and culture. "But now Russia is the aggressor for the whole world, and we protest it."

Ukrainian nationals in Taiwan and supporters have also staged a march in Taipei to protest the Russian invasion.

- by Frank Jordans of AP