Boris Nemtsov, the Russian opposition leader, was shot dead near the Kremlin two years ago.
Thousands of people are marching in Moscow to remember Russian opposition leader, Boris Nemtsov, who was shot dead outside the Kremlin in 2015.
Nemtsov, a reformer, democrat and a deputy prime minister under former President Boris Yeltsin, was a fierce critic of President Vladimir Putin.
Five Chechen men went on trial for the killing in October.
They deny the charges and Nemtsov’s relatives fear whoever ordered the murder will never be found.
Separately on Sunday, anti-Kremlin activist Ildar Dadin, the first person jailed under new laws targeting protests, was released from a Siberian prison. The Supreme Court had overturned his conviction on Wednesday.
He says he was tortured by staff while in prison, an accusation officials deny.
BBC Moscow correspondent Sarah Rainsford says the marchers, numbering thousands rather than tens of thousands, are moving slowly towards a square in the city.
Our correspondent says the marchers have not been given permission to travel to the Moskvoretsky bridge where Nemtsov was shot dead, but some will probably go anyway.
The bridge has already been lined with flowers of tribute.
One of the marchers, Galina Zolina, told Agence France-Presse: «We came to pay tribute to the honesty and bravery of Boris Nemtsov. We want to show the authorities that we haven’t forgotten. »
The rally appears peaceful, although green ink was thrown into the face of Putin critic and former PM Mikhail Kasyanov as he marched on Sunday.
Rallies are also expected in St Petersburg and other cities.
Nemtsov, who was 55, was shot in the back as he walked home from a restaurant with his Ukrainian girlfriend late at night near the Kremlin on 27 February 2015.
He had earlier been at the radio station Ekho Moskvy, calling on listeners to join a protest. He had accused Russia’s president of launching an illegal war with Ukraine, prompting Western sanctions and an economic crisis.
He had also been planning to publish a file on Russian involvement in eastern Ukraine.
Those who marched on Sunday carried flags, posters and quotes from Nemtsov. Some read «The war with Ukraine was a crime of Putin», «Russia without Putin» and «I am against the annexation of Crimea».
Nemtsov’s political allies believe the killing was meant to terrify them into silence.
Opposition activist Vladimir Kara-Murza earlier urged people to join the anniversary rallies.
Mr Kara-Murza is recovering abroad after an illness that left him in a medically induced coma. His symptoms were similar to a near-fatal illness in 2015 that he believed was the result of deliberate poisoning.
The trial of the five Chechens for Nemtsov’s murder began in October.
The suspect who investigators say carried out the killing, Zaur Dadayev, was an officer under the command of pro-Moscow’s Ramzan Kadyrov, the leader of Russia’s Chechen Republic in the volatile North Caucasus.
The Chechen leader has denied any link to the killing.
Boris Nemtsov murder: Who are the suspects?
President Putin called the murder «vile and cynical» and vowed that those responsible would be held to account.
Russia has seen several killings of high-profile politicians and journalists.
But the country has a long history of prosecuting alleged hit-men and then failing to follow the chain of command upwards to discover who ordered the murder or why, our correspondent says.
