A Russian state security expert has died while attempting to defuse an explosive device in a Moscow street.
The explosives expert tried to defuse the device
The blast early on Thursday occurred less than a week after a double suicide bomb attack at a music festival in the city, which killed 14.
Moscow police said that they detained a woman acting suspiciously as she tried to bring a rucksack into a restaurant in the centre of the city.
The rucksack was thrown into the street, but while a FSB state security expert was examining it, it exploded, killing him and shattering windows in nearby houses.
Police say the device may have been set off remotely, and are searching for a male accomplice who apparently escaped.
They also said they had identified the woman as a 22-year-old resident of Chechnya. No group has claimed responsibility for the attempted attack.
Moscow authorities have linked the incident to the music festival attack.
The explosion comes as the rapporteur on Chechnya for the Parliamentary Assembly of the Council Europe, Swiss member of parliament Andreas Gross, is to meet Russian officials for talks on Chechnya.
Security staff at the Imber restaurant on Tverskaya Street first raised the alarm shortly after midnight, when they detained the woman as she attempted to enter the restaurant.
The woman had reportedly been seen trying to enter several bars filled with customers, and witnesses reported that she had seemed nervous.
The device was first probed by a remote-controlled robot
Police were called and they cordoned off the area, while local residents were warned not to leave their homes.
A police robot inspected the rucksack and handled it five times without incident.
But when the explosives expert approached the bomb, it blew up.
Police estimated that it contained the equivalent of 400 grams (14 ounces) of TNT.
Despite the expert's death, BBC correspondent Nikolai Gorshkov in Moscow said police are still pleased as it is the first time that a potential suicide bomber has been caught alive.
They hope to learn valuable information about how such bombers are recruited and their methods, our correspondent adds.
Two women carried out Saturday's attacks, which the authorities have blamed on Chechen separatists.
Our correspondent says that there are growing suspicions in Moscow that the city has become the target of a well-planned suicide bombing campaign.
On Thursday a spokesman for Chechen president Aslan Maskhadov told the BBC that he hoped the meeting between EU representative Gross and Russian officials would lead to the EU pressing Russia to find a peaceful solution to the conflict.
The spokesman, Osman Firzaouli, also expressed his concern for future Chechen generations who knew nothing but the bloody conflict between Russia and Chechen separatists.
"One problem is that a young generation who grew up through the war in Chechnya, they have no education and no life experience, only disaster and the feeling of despair," he said.
"[As] a result of the Russian brutality in Chechnya we are afraid that in the future the young generation of Chechnya will go out of control - both Russian and Chechnyan control."