Holding placards declaring "I am not afraid," thousands of Russians marched in Moscow on Sunday in memory of Kremlin critic Boris Nemtsov, whose murder has widened a split in society that some say could threaten Russia's future.

Families, the old and young walked slowly, with many carrying portraits of Nemtsov, an opposition politician and former deputy prime minister who was shot dead while walking home from a restaurant in central Moscow on Friday night.

"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, said before the march.