AKIPRESS.COM - Tens of thousands of Russians marched through central Moscow on Sunday, carrying banners declaring "Boris!" (Fight!), "He died for the future of Russia" and "Heroes never die" in memory of murdered opposition politician Boris Nemtsov.

People walked slowly with many holding portraits of the former deputy prime minister who was shot dead while walking home from a nearby restaurant on Friday night. The authorities have suggested the opposition itself may have been behind his shooting in an attempt to create a martyr and unite the fractured movement.

His supporters have blamed the authorities. "If we can stop the campaign of hate that's being directed at the opposition, then we have a chance to change Russia. If not, then we face the prospect of mass civil conflict," Gennady Gudkov, an opposition leader, told Reuters.

Police said 21,000 people attended the march. The organizers put the numbers at tens of thousands, but attendance appeared smaller than the 50,000 people the opposition had hoped for.

People walked in the rain within view of the Kremlin's red walls and past the spot, now covered in flowers, where Nemtsov was shot dead.

Putin has vowed to pursue those who killed Nemtsov, calling the murder a "provocation".

National investigators who answer to the Russian leader offered a 3-million-rouble reward, around $50,000, for information on Nemtsov's death. They say they are pursuing several lines of inquiry, including the possibility that Nemtsov, a Jew, was killed by radical Islamists or that the opposition killed him to blacken Putin's name.

Nemtsov's funeral is due to be held on Tuesday in Moscow.