Two female suicide bombers have blown themselves up at a rock festival just outside Moscow, killing at least 15 people and injuring more than 50.
The bombs were detonated some way away from the main crowd
Interior Minister Boris Gryzlov blamed the attacks on Chechen separatists, saying a Chechen passport had been found on one of the bombers.
But a Chechen spokesman, Salambek Maigov, told a Russian radio station that the leadership of his homeland was not involved.
The all-day festival featuring many of Russia's most popular bands at the Tushino airfield in north-western Moscow was packed with a crowd of about 40,000 people, many of them youngsters, when the bombs went off.
At first I thought it was a giant firecracker, then I realised it was an explosion
Several Moscow clinics are being kept busy overnight treating patients with shrapnel wounds and severe burns, some of whom are in critical condition.
Medics have warned that the death toll could rise further.
Packed with nails
The airfield was hosting the "Krylya" (Wings) festival - a popular summer event for young music fans in Moscow.
The first blast happened as people queued near the concert entrance at 1439 local time (1039 GMT) on Saturday.
A woman detonated an explosives belt near an admissions booth when police tried to stop her entering.
Police say she was killed outright along with one other person and that many others were injured. Although the authorities say that it could have been much worse since the bomb belt failed to explode properly.
History of Chechen attacks
5 June 2002 - 18 people killed in suicide bomb attack on Russian air force bus
14 May 2003 - 16 people killed in suicide bomb attack at religious festival in Chechen town Iliskhan-Yurt
12 May 2003 - 61 people killed in suicide truck bomb attack on government complex in Chechen town of Znamenskoye
27 December 2002 - 80 killed as suicide bombers drive vehicles packed with explosives into government building in Grozny
23-26 October 2002 - 129 hostages and 41 Chechen guerrillas killed in Moscow theatre siege
19 August 2002 - 118 Russian soldiers killed as Chechen rebels shoot down a transport helicopter
Fifteen minutes later there was a second, more powerful explosion as another female bomber blew herself up just metres from the main entrance.
The BBC's correspondent in Moscow Sarah Rainsford said that most of the victims were killed in the second blast. One witness said that after the first blast police told spectators to leave by the other gate - where the second bomb went off.
Both bombs had been stuffed with screws and nails, intended to cause maximum damage.
"At first I thought it was a giant firecracker, then I realised it was an explosion," eyewitness Vadim Trushkin told the Associated Press news agency.
Mobile calls blocked
Rescue teams were flown in by helicopter and the wounded taken to nearby hospitals.
But the police say the devastation could have been far worse, had vigilant officers not stopped the women at the gate.
The concert continued with many unaware the attack had taken place
Our correspondent said that as panic reigned on the streets outside, many festival-goers inside the air base remained unaware of events.
The organisers decreed that to avoid a panic stampede the show must go on and did not make any announcement about the incident, allowing the performances to proceed.
The BBC's Nikolai Gorshkov in Moscow said that the authorities blocked all mobile telephone calls to the area to allow the audience to enjoy the rest of the concert oblivious of the carnage.
Then slowly, but surely the concert goers were evacuated onto waiting coaches.
Our correspondent Sarah Rainsford says no one had yet claimed responsibility for this attack but connection with Chechnya would be high on people's minds.
There have been heightened fears of attacks by Chechen militants since the hostage siege at a Moscow theatre last year.
That resulted in the death of 129 hostages and 41 guerrillas, who had included women armed with explosive belts, after Russian special forces used noxious gas to disable the hostage-takers.
Russian President Vladimir Putin has been informed of the incident.
On Friday, Mr Putin ordered a local presidential election to be held in Chechnya on 5 October.
"I presume that this inhumane situation, this terrorist act, is linked with the staging of this event," Mr Gryzlov said.
However, the BBC's Russian affairs analyst Stephen Dalziel says there is unlikely to be a direct link, given that an attack of this nature would need considerable planning.
The BBC's Nikolai Gorshkov says President Vladimir Putin had vowed that such attacks acts by what he called a small hard core group of fighters would not throw him off course.
But our correspondent says that some politicians say unless the Kremlin starts talks with the rebels and prosecutes those responsible for human rights abuses in Chechnya, Moscow and other Russian cities would never be safe.