A suspected suicide bombing near Red Square in Moscow has left six people dead and wounded several others.
Russian TV pictures showed a car wrecked in the blast
The blast happened on a busy street only a few hundred metres from the Kremlin in the heart of the city.
In a speech soon afterwards, President Vladimir Putin said "terrorists" threatened the nation's development.
The attack may have been aimed at government buildings, two days after Mr Putin's supporters won legislative elections.
It follows last week's suicide bombing on a train in southern Russia that killed dozens of people and which officials blamed on Chechen rebels.
The Moscow bomb went off shortly before 1100 local time (0800 GMT) outside the National Hotel, yards from the capital's main shopping street, Tverskaya Street.
Thirteen people were reportedly wounded.
A Mercedes sedan was destroyed in the explosion, but it is unclear whether the explosion was a car bomb.
Moscow mayor Yuri Luzhkov described the attack as a botched attack by at least one, but probably two, women suicide bombers.
The bomber or bombers had earlier asked a passer-by the way to the State Duma - the lower house of parliament, he said.
"Evidently, the bomb went off by accident," he was quoted as saying by Interfax news agency.
"The National Hotel was not the place where the
suicide bombers had planned to stage the explosion."
Police spokesman Yevgeny Gildeyev said police investigators were becoming increasingly persuaded the blast was related to terrorism, rather than to a business dispute, AP said.
The Federal Security Service (FSB) has also said it considers the bombing a terrorist act, according to Russian agencies.
The hotel sits on a corner opposite an entrance to Red Square and the Kremlin. First and second-floor windows along the street were blown out.
"We felt a kind of whoosh, heard a bang, and saw smoke," an unidentified witness told Russian state television, according to Reuters.
A Reuters correspondent reports seeing the severed head of a woman lying on the pavement next to a briefcase, as well as flesh on the snowy pavements.
Television pictures also showed a body lying outside the hotel, behind a destroyed car.
Police cordoned off the area and brought in a bomb disposal robot to locate undetonated explosives reportedly found on one body at the scene.
Bomb disposal experts then carried out two controlled explosions, one on a handbag apparently suspected of containing explosives.
Shortly after the attack President Putin addressed regional leaders at a Kremlin meeting to commemorate the 10th anniversary of the nation's constitution, which will be celebrated on Friday.
"[The constitution] is a foundation for the development
of a free market economy, democracy, and the development of the nation as a whole and the preservation of its
territorial integrity," he reportedly said.
"The actions of criminals,
terrorists, which we have to confront even today, are aimed against all that."