A "Black Widow" suicide bomber planned a terrorist attack in central Moscow on New Year's Eve but was killed when an unexpected text message set off her bomb too early, according to Russian security sources.

The unnamed woman, who is thought to be part of the same group that struck Moscow's Domodedovo airport on Monday, intended to detonate a suicide belt near Red Square on New Year's Eve in an attack that could have killed hundreds.

Security sources believe a message from her mobile phone operator wishing her a happy new year received just hours before the planned attack triggered her suicide belt, killing her at a safe house.

Islamist terrorists in Russia often use mobile phones as detonators. The bomber's handler, who is usually watching their charge, sends the bomber a text message in order to set off his or her explosive belt at the moment when it is thought they can inflict maximum casualties.

The dead woman has not been identified, but her husband is apparently serving time in jail for being a member of a radical Islamist terror group.

Security sources believe the New Year's Eve bomber and the airport bombers may have been members of a suicide squad trained in Pakistan's al-Qaida strongholds which was sent to target the Russian capital's transport system.

Nobody has been arrested in connection with Monday's bombing, which left 35 people dead. Police are trying to identify the severed head of a male suicide bomber recovered from the scene.

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