Story highlights

  • Boris Nemtsov shot at least four times from a car
  • Nemtsov was an outspoken critic of President Vladimir Putin
  • Putin offered his condolences and called the murder a provocation
  • Investigative Committee, answering to Putin, opened an investigation
Tens of thousands of people have marched through Moscow in memory of Kremlin critic Boris Nemtsov, who was gunned down in the Russian capital on Friday night.
More than 70,000 people turned out in central Moscow on Sunday, many carrying Russian flags and slowly marching through an avenue alongside River Moskva, one of the organisers said, but police estimated the crowd at more than 16,000.
Al Jazeera's Rory Challands, who is reporting from Moscow, said security is "very tight" for the rally.
Our correspondent is also reporting that a Ukrainian member of parliament, who attended the march, has been detained.

On Saturday, thousands of people laid flowers and lit candles on a bridge near the Kremlin where Nemtsov, a former deputy prime minister, was shot to death.
National investigators who answer to President Vladimir Putin say they are pursuing several lines of inquiry, including the possibility that Nemtsov, who was 55, was killed by Muslim attackers or that the opposition killed him to blacken the president's name.
Kremlin critics who were killed or died in suspicious circumstances
  • Boris Berezovsky, 67, a former oligarch and fierce foe of Russian President Vladimir Putin. Found hanged in a bathroom at his home in the UK on March 23, 2013.
  • Anna Politkovskaya, 48, a journalist, is shot to death at the entrance to her apartment block in central Moscow on October 7, 2006.
  • Alexander Litvinenko, 43, former intelligence officer turned Putin critic dies after allegedly drinking tea laced with radioactive on November 23, 2006.
Putin's opponents say such suggestions show the cynicism of Russia's leaders as they whip up nationalism, hatred and anti-Western hysteria to rally support for his policies on Ukraine and deflect blame for an economic crisis.
"It is a blow to Russia. If political views are punished this way, then this country simply has no future," Sergei Mitrokhin, an opposition leader, said of Nemtsov's murder.
Putin has described the killing as a "provocation", and told Nemtsov's 86-year-old mother, Dina Eidman, that the killers would be found and punished.
He also promised to do everything possible to bring to justice those responsible for Nemtsov's killing.
"Everything will be done so that the organisers and perpetrators of a vile and cynical murder get the punishment they deserve," Putin said in a telegram to Nemtsov's mother published on the Kremlin's website.
He said Nemtsov's death was an irreparable loss and that he had "left his trace in Russia's history, in politics and public life".
Nemtsov was one of the leading lights of an opposition struggling to revive its fortunes three years after mass rallies against Putin failed to prevent him from returning to the presidency after four years as prime minister.
Putin has now been Russia's dominant leader since 2000, when ailing President Boris Yeltsin chose the former KGB spy as his successor, a role Nemtsov had once been destined to play.

  Read more: Boris Nemtsov's last walk

Supporters pay tribute to slain Russian opposition leader
Many opposition leaders have been jailed on what they say are trumped-up charges, or have fled the country.
Nemtsov had hoped, however, to start the opposition's revival with a march in Marino on the outskirts of Moscow on Sunday to protest against Putin's economic policies and what they see as Russia's involvement in the separatist war in east Ukraine.
The Kremlin denies any role in the fighting.
Nemtsov had said in an interview that he feared Putin may want him dead because of his outspoken criticism of Russia's role in Ukraine.
Ukrainian President Petro Poroshenko said Nemtsov had told him about two weeks ago that he planned to publish evidence of Russian involvement in Ukraine's separatist conflict.
"Someone was very afraid of this... They killed him," Poroshenko said in televised comments shown in Ukraine.
Organisers said more than 70,000 people turned out in central Moscow on Sunday to mourn Nemtsov, but police estimated the crowd at 16,000 [EPA]
 
People visited the site where Nemtsov was shot to death near the Kremlin and Red Square in central Moscow [Reuters]