Thousands of Russians marched through Moscow on Sunday shouting slogans such as "Russia will be free!" and "Putin is war!" to mark two years since opposition leader Boris Nemtsov was gunned down outside the Kremlin.

Nemtsov, a former deputy prime minister, was a fierce critic of President Vladimir Putin. His Feb. 27, 2015, death, in what appeared to be a contract killing, sparked an outpouring of anger and fear in Russia's beleaguered opposition movement.

The memorial protest was the largest opposition gathering since a similar march for Nemtsov in 2016. Organizers put the number of participants at just over 15,000. The police, known for underestimating attendance at political rallies, said about 5,000 people showed up.

"It's very important that after two years people continue to come out and show their solidarity with the ideas for which Boris Nemtsov fought for and gave his life," opposition activist Ilya Yashin, who was Nemtsov's friend and colleague, told the Interfax news agency.