The suicide bomber who killed 35 people at Moscow's Domodedovo airport may have been part of a group despatched by militants in the Northern Caucasus to bomb the capital, reports said Tuesday.
The Kommersant daily, citing its own sources, said the Russian special services became aware of the risk of an attack when a small building on the site of a Moscow sports club was completely destroyed by an explosion late on December 31st.
It said that the explosion was caused by a woman from the Northern Caucasus who had accidentally blown herself up due to carelessness with explosives.
"Militant leaders had despatched women to carry out an attack on the night of New Year," it said. "But one of them exploded her charge prematurely."
"It is not excluded that she did not come to Moscow alone but with several groups of suicide bombers. And a second woman blew herself up yesterday," said the paper.
It said that the woman who blew herself up on December 31 had been the wife of a man serving a jail term for participation in a North Caucasus militant group.
The Interfax news agency carried a similar report, adding that the authorities later arrested the female companion of the dead woman who had fled to the southern city of Volgograd.
The authorities also then started a search for three suspects from Chechnya who were believed to have been preparing another suicide bomber.
The trio then accompanied the woman to Domodedovo airport Monday, where she set off her charge. They then disappeared without trace.
State-run RIA Novosti also quoted a security source as saying Tuesday that the bomb appeared to have been set off by a female suicide bomber.
The reports again bring to mind the past attacks blamed on so-called "Black Widows" from the Northern Caucasus -- women who lost their militant husbands and then volunteered for suicide bombings.
The Russian capital has been repeatedly rocked by attacks over the last years blamed on militants from the Northern Caucasus region, where Russia has for years been battling an Islamist insurgency.
Double bombings carried out by two female suicide bombers on the Moscow metro on March 29, 2010 killed 40 and wounded more than 100.