A newspaper close to Russia's FSB security service published what it claimed was a warning to Moscow police issued in December that said there was credible intelligence that a suicide squad made up of three women and one man from Chechnya was headed to Moscow.

The memo said the team had spent time in Pakistan and Iran and that one of the women had a relative with a flat in Moscow that might be used as a bomb making factory. Another group of five Islamist militants trained in Pakistan was also expected to cross into Russia soon, it added.

An al-Qaeda linked website said that the group Islamic Caucasus Emirate, led by the rebe Doku Umarov, was poised to claim it had staged the attack. It said that Russia's harsh military measures against independence activists in the Caucasus had provoked the attack. It said: "You disbelievers are the firewood of Hell. You will enter it."

The daily Kommersant newspaper said security service officials were alerted to the extent of the threat when a woman accidentally blew herself up on New Year's Eve in Moscow. It later emerged that her husband was in jail for being a member of an Islamist terror group and that she and a girlfriend had been sent to Moscow from the internal Muslim republic of Dagestan to commit an act of terror.

Russian media published a grisly picture of the male terrorist's severed head that was being circulated around police and security services in the troubled mostly Muslim North Caucasus region to see if anyone recognised him.