Ten people have been killed and at least 50 injured by a female suicide bomber in a central Moscow car park.
Local television footage showed a blazing car parked between a large shopping centre and the entrance to a metro station, with several bodies lying on the pavement. Tass news agency said a number of children were among the injured.
An Islamist group claimed responsibility for the bombing at the crowded Riga metro station and vowed there would be more attacks on "infidel" Russia, according to a statement published on a website.
"We in the Islambouli Brigades announce our responsibility for this operation... which comes in support of Muslims of Chechnya," said the statement signed by the group, which had earlier also claimed responsibility for last week's plane crashes in Russia.
Mayor Yuri Luzhkov said the woman had tried to enter a metro station, Riga Station, that would have been crowded towards the end of the evening rush hour.
"She was at the door when she saw two policeman. She was scared and turned and decided to destroy herself," he said. "Up to 1 kg of explosive was used," the mayor told reporters at the scene. "This is an unusual amount of explosive for a woman suicide bomber. There was a desire to cause maximum damage."
He said four children and 11 women were among the injured. Seven people died immediately in the blast, including the bomber. Another person died later in hospital.
Police earlier said the bomb had been packed with metal bolts.
The explosion came on the last day of the summer school holidays when parents and their children were certain to be doing last-minute pre-school shopping.
Exactly a week ago, 90 people died when two Russian airliners crashed almost simultaneously in what officials believe was the work of suicide bombers.
Russia officials have described that air disaster as a terrorist act and have pointed the finger at Chechen rebels who have been battling Moscow rule for more than a decade.
Hours before the air crashes, a bomb had exploded at a bus stop in southern Moscow injuring three people. Tass quoted its police source as saying the explosive device used in southern Moscow and today's bomb were similar.
In July last year two women suicide bombers, thought to be Chechens, killed 15 other people when they blew themselves up at an open-air rock festival at a Moscow airfield.
Six months later another female bomber killed five people near the Kremlin.
Many bombings in Russia in recent years have been linked to the Chechen conflict, but some have been blamed on organised crime.