Police said they suspected Tuesday's blast was set off by at least one female bomber who wore a belt packed with explosives and ballbearings.
Her blown-off head was discovered lying on a busy pavement on Moscow's Mokhovaya street facing the Kremlin.
A second undetonated device was discovered on a woman's body after police had secured the site.
"There may have been two suicide bombers," Moscow Mayor Yury Luzhkov said.
Officials said the bomber had apparently tried to target the State Duma lower house of parliament building that was a few dozen metres away.
Police said they were looking for another suspect who might have taken part in the attack and had the features of a person from the Caucasus - the code used to indicate the blast was carried out by Chechen rebels.
"My car was covered with chunks of human flesh. There were two girls covered in blood and human flesh who were crawling through the snow"
Moscow bomb witness
The ITAR-TASS news agency quoted an unnamed security official as saying Russian authorities had identified one of the bombers as a woman for whom they had been looking since July.
"She went through training in one of the rebel camps," the official said in apparent reference to Chechen resistance fighters.
Putin launched the Chechen invasion in October 1999, but the brutal war did not feature as a campaign topic in recent Duma elections in which pro-presidential forces stormed to power.
Officials said the 14 wounded included several students from Moscow State University and that five people were in serious condition.
Witnesses described scenes of chaos breaking into the heart of Moscow at the start of a regular business day amid posh hotels, shops and government buildings.
"For five minutes (after the blast) it went all quiet as the bodies lay on the ground. Then police and ambulance cars arrived," said Vladimir Khomerkov, 45.
"A businessman who had an expensive coat on was lying on the ground with his head torn off. It was just lying there," he said.
Reports quoted a police official as saying two women had walked up to a passer-by and asked "Where is the Duma?" - referring to the parliament chamber that faced re-election on Sunday. A blast went off, moments later.
Brutal Chechen war
It was not immediately clear if Putin was inside the Kremlin at the time of the explosion.
Putin was elected president
after his brutal Chechen invasion
Putin has been identified closely with the war in Chechnya. He launched the brutal war while still serving as prime minister in October 1999, in a move that proved very popular.
Support for the war has since cooled and much of Russia's state-controlled media make only limited mention of the conflict.
The Moscow blast went off just two days after Russia took extraordinary security measures to make sure the Duma elections went off safely.
Two days before the vote, a bomb attack struck a train in a southern Russian region, travelling near Chechnya, killing 44 people and injuring more than 170 others.