MOSCOW -- Thousands of people have marched in Moscow and staged protests in other Russian cities, marking the anniversary of the killing of Boris Nemtsov, a charismatic Kremlin critic and former deputy prime minister who was gunned down five years ago near the Kremlin.
The February 29 demonstrations were the biggest political protests in Russia since last summer, when several weeks of anti-government meetings challenged the authorities in Moscow over local city council elections.
The protests come as lawmakers and Kremlin officials prepare for a national vote on major changes to the country's constitution unveiled last month by President Vladimir Putin.
Chants of "Putin is a thief" and "Russia without Putin" echoed among the crowd in the Russian capital, with many demonstrators carrying Russian flags and flags of the political party Nemtsov was affiliated with. Others held photographs of Nemtsov, and signs reading "Propaganda kills" and "Say no to constitutional amendments."
On the bridge where Nemtsov was killed on February 27, 2015 -- just a couple hundred meters from the Kremlin's walls -- people lit candles and placed flowers, photographs, and small Russian flags.
The protests "are about freedom in general, it's not just about the life of a single person anymore," one unnamed woman told RFE/RL's Russian Service as she went to lay a bouquet of white roses at the site. Nemtsov "was a symbol of the overall social movement, about how to live more justly."
One group held a banner that read "Ukraine, we are with you" -- a reference to the six-year war in eastern Ukraine, pitting Ukrainian government forces against Russia-backed militias.
"We don't need a cult, we need a leader," one participant told Current Time at the Moscow rally. "We need a normal economy that's right for a giant country like ours.... Education, science, social welfare, we're in last place in so many rankings. It's a disgrace."
"It's not only about Nemtsov, it's about everything that's going on in our country," another unnamed man told Current Time. "In particular, it's about what kind of regime we have in place, how our law enforcement and judiciary is organized and all the legal cases that are going on [against opposition figures]. I think one has to speak up about that and to show one's position."
White Counter, a nongovernmental organization that estimates attendance at political protests, said more than 22,000 people had participated in the Moscow demonstration, which had been authorized by city officials. Moscow city police estimated 10,500 people attended.
The Kremlin had no immediate comment as the demonstrations got under way.
No mass arrests were reported in Moscow or elsewhere, though there were scattered reports of activists being detained.
In Russia's second-largest city, St. Petersburg, an estimated 8,000 people marched to mark the anniversary. OVD-Info, a nongovernmental organization that monitors police arrests at political protests, said eight people were detained there, though it was unclear on what charges.
Other, smaller events took place in Russia's second-largest city, St. Petersburg, Novosibirsk, and many other cities across the country. In the Pacific port of Vladivostok, several people were detained by the police as they held placards commemorating Nemtsov.
A handful of arrests were reported in Moscow and other locations, according to OVD-Info, a nongovernmental organization that monitors police arrests at political protests. Five demonstrators were detained in St. Petersburg, the organization said.
"Nemtsov fought for a free Russia. But in the five years since his death, Russia has become even more authoritarian," Assol Trubetskaya, the head of a local political organization in the Siberian city of Omsk, told RFE/RL's Russian Service.
Democracy activist Vladimir Kara-Murza thanked those who turned out in Twitter post. "Lots of people today. Thanks to everyone who came. A person is alive as long as his memory lives," Kara-Murza wrote about his friend and political mentor, Nemtsov.
Some opposition supporters said they planned to use the event to protest proposed amendments to the country's constitution. Critics say the planned changes are aimed at extending Putin's grip on power after his current presidential term ends in 2024.
The amendments unveiled by Putin last month are the most substantive changes to the constitution since its adoption in 1992.
The Kremlin has set April 22 as the date to hold a national referendum on the proposed constitutional changes, which include a proposal that some critics say opens the door for Putin to remain in power beyond the end of his current term in 2024.
Protest organizers, including anti-corruption crusader Aleksei Navalny, called for a mass turnout, calling it a test of Russians' willingness to push back against Putin's proposals.
"The Kremlin is going to look at how many people attend the Nemtsov march," Navalny said on February 28.
A deputy prime minister under Putin's predecessor, Boris Yeltsin, Nemtsov was a charismatic and vocal critic of Putin. He was shot at close range on the Bolshoi Moskvoretsky Bridge, a stone's throw away from the Kremlin, as he walked with a female companion.
In June 2017, a Russian court sentenced a former Chechen military officer, Zaur Dadayev, to 20 years in prison for killing Nemtsov.
Four other Chechens were found guilty of involvement in the killing and sentenced to prison terms ranging from 11 to 19 years.
But critics, including relatives and colleagues of Nemtsov, say the Russian authorities failed to determine who ordered the killing.
Some have expressed suspicions that the killing was ordered by someone within the inner circles of Putin or Chechen leader Ramzan Kadyrov.
A report from the Organization for Security and Cooperation in Europe (OSCE) on February 20 called for "a new and full investigation" into Nemtsov's slaying.
The report, by the OSCE Parliamentary Assembly's special rapporteur, Margareta Cederfelt, said shortcomings in Russia's original investigation left many questions unanswered.
"His death was a tragedy for Russia and had a strong impact on the political climate, spreading fear and possibly opening up for further attacks and repression," the report said.