The pro-Moscow President of Chechnya, Akhmad Kadyrov, has been killed in a bomb attack in the capital, Grozny.
People fled from the scene in terror
Reports of the total number killed in the blast at the city's Dynamo stadium vary between six and more than 30.
Russian President Vladimir Putin said Mr Kadyrov was a true hero and vowed revenge for the attack thought to have been carried out by Chechen rebels.
Mr Kadyrov's death is being seen as a huge blow to Moscow's attempts to restore order in the troubled republic.
Chechen rebels have been fighting for independence from Russia for more than a decade.
Security forces throughout Chechnya have been placed on high alert and Russia's Itar-Tass news agency has reported that five people have already been detained on suspicion of involvement with the attack, according to interior ministry officials.
Mr Kadyrov's assassination has drawn broad international condemnation.
A White House spokesman said Washington resolutely rejected all acts of terrorism, while the European Commission described the blast as a " heinous attack".
Mr Kadyrov was fatally wounded when a device exploded at 1035 (0635 GMT) during a ceremony marking victory in World War II.
A spokesman for Russia's emergency situations ministry said the bomb had gone off in a VIP seating area of the packed Dynamo stadium.
There is uncertainty over the fate of the commander of Russian troops in Chechnya, Gen Valery Baranov, who was also in the stadium at the time.
Officials have denied reports that he was killed by the blast and said he was fighting for his life in hospital.
Russian television showed chaotic scenes as panic-stricken spectators ran from the scene and brown smoke rose from the debris of the stand.
One man was seen carrying an injured child to safety, while bursts of gunfire rang out.
Born in Kazakhstan in 1951
Studied Islam and became Chechnya's mufti in 1995
Sacked as mufti in 1999 after falling out with separatist leader Aslan Maskhadov
Appointed as head of pro-Moscow administration by President Putin
The emergency ministry spokesman said a second device had been found following the evacuation of the stadium.
Chechen interior ministry officials quoted by the AFP news agency said at least 32 people had been killed and 46 injured.
Mr Putin, speaking at the end of the Victory Day parade in Moscow, said: "There can be no doubt that retribution is inevitable for those whom we are fighting today. It will be unavoidable for terrorists."
He said Mr Kadyrov's work had proven there was a difference between
"bandits, terrorists and the Chechen people".
He has appointed Chechnya's Prime Minister Sergei Abramov as acting president.
Russia has been fighting separatists in Chechnya since the republic first tried to break away in the 1990s.
Moscow has reimposed its rule in Grozny, but rebel attacks have continued, both in Chechnya and elsewhere in Russia.
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