The Moscow airport blast that killed 35 people may have involved a female suicide bomber from Russia's predominantly Muslim North Caucasus, RIA Novosti quoted a security source as saying on Tuesday.
"The explosion occurred the moment the presumed female suicide bomber opened her bag," the state-run news agency quoted the unnamed security official as saying.
"The terrorist was accompanied by a man. He was standing beside her and (the blast) tore off his head."
According to Interfax, one of the eyewitnesses also said he had seen how the hand baggage of a woman dressed in black exploded.
It said the security agencies were aware of the possible terror attacks, and were looking for 'Black Widows' of the slain militants from the Caucasus, who had carried out all suicide attacks in past, including twin blasts in Moscow metro stations in March 2010.
Russian investigators said on Monday they had found a head of "Arab appearance" that was initially presumed to have belonged to the suicide bomber.
The unnamed security source said the blast bore the hallmarks of an attack carried out by North Caucasus militants.
"This act of terror followed the classic scheme used by terrorists who come from the North Caucasus," said the security official.