Thousands of protesters have been marching through the streets of Moscow to honour murdered Russian opposition leader Boris Nemtsov.
Organisers said more than 70,000 people joined the rally to mourn the former deputy prime minister, who was gunned down near the Kremlin on Friday.
Many of the demonstrators carried portraits of Putin critic Mr Nemtsov, as well as placards declaring "I am not afraid" and "He died for Russia's future".
Opposition leaders said the protest was aimed at stopping a "campaign of hate" directed at those who question President Vladimir Putin's rule.
"If we can stop the campaign of hate that's being directed at the opposition, then we have a chance to change Russia," said Gennady Gudkov, an opposition leader.
"If not then we face the prospect of mass civil conflict. The authorities are corrupt and don't allow any threats to them to emerge. Boris was uncomfortable for them."
Police estimated the crowd on Moscow's streets was around 16,000 people.
Mourners earlier laid flowers and lit candles on a bridge near the Kremlin where Mr Nemtsov was gunned down.
The 55-year-old was shot in the back several times just before midnight on Friday as he was walking home from a restaurant in the centre of the city.
The killing was the latest in a string of murders of opposition figures in Mr Putin's 15 years in power and recalls the shooting of anti-Kremlin reporter Anna Politkovskaya, who was killed in October 2006.
Mr Putin has condemned the death and blamed the latest killing on enemies trying to discredit the Kremlin.
In a message to Mr Nemtsov's mother, he said: "Everything will be done so that the organisers and perpetrators of a vile and cynical murder get the punishment they deserve."
Amnesty International said: "There is already a list of unsolved political murders and attacks in Russia. We cannot allow Boris Nemtsov to become just another name on this list."
'Tireless advocate'
The White House has demanded that the investigation is "prompt, impartial and transparent".
President Barack Obama, who met Mr Nemtsov in 2009, described him as a "tireless advocate" for the rights of Russian citizens, and cited his work in fighting corruption.
British prime minister David Cameron said the Russian people had been deprived of a champion of their rights and that Mr Nemtsov was greatly admired in Britain, not least by Margaret Thatcher.
"I am shocked and sickened by the callous murder of Boris Nemtsov as he walked in the heart Moscow," he said.
"This despicable act must be fully, rapidly and transparently investigated, and those responsible brought to justice."
Investigators say gunmen fired at least eight shots from a car as Mr Nemtsov walked with a woman named by Russian media as 23-year-old Ukrainian model Anna Duritskaya, who was unhurt.
Footage aired by Russian TVC channel from a distant camera showed the suspected killer running along the road and jumping into a waiting car which then sped off.
Former President of Georgia, Mikheil Saakashvilli, says he was not surprised by the killing under Putin's rule.
Originally posted at 13.26
