The fifth bomb explosion in Russia in 17 days followed the deadly pattern of three of the previous ones: a bomb blew up residents of an apartment block in their sleep, this time in a town just to the north of the turbulent North Caucasus region, Volgodonsk.

	Who is to blame? What Russia can do Timeline: The blasts which shook Russia

The Russian authorities are now openly blaming militants in the breakaway republic of Chechnya for the bombs.

The new Prime Minister Vladimir Putin said he would ask the Chechen government to hand over men he said were international terrorists.

Yet there are still many unanswered questions.

In particular the two main leaders of the recent rebellions in the North Caucasian republic of Dagestan, the Chechen fighter Shamil Basayev and his Arab comrade-in-arms Khatab, have both denied responsibility for the acts of terror and said that they would never attack Russian civilian targets.

Dagestan link

The only person so far to claim responsibility for the bomb blasts telephoned the Russian news agency Itar-Tass on Wednesday and said he was from an unknown group called the Liberation Army of Dagestan.

Russia sends more troops to Dagestan

Some Russian politicians said they thought it was a front for the Chechnya-based guerrillas.

The Chechen president Aslan Maskhadov pointed out that this "army" could be one of many groups fighting the Russians in Dagestan.

They include Sheikh Baggaudin Mohammad who heads the so-called Islamic Army of the Caucasus in Dagestan and "General" Dzharulla, a self-proclaimed adherent of the strict Wahabi form of Islam who led a rebellion in the Dagestani villages of Karamakhi and Chabanmakhi, which were seized by Russian forces last week.

Revenge killings

The caller to Itar-Tass did say the bombs were an act of revenge for the bombing of Karamakhi.

The village has been a stronghold of militant Islam for almost two years - and it is from there that the Arab fighter Khatab has taken a wife.

Shamil Basayev also made a revealing remark in an interview he gave on September 9 to the Czech newspaper Lidove Noviny:

"The latest blast in Moscow is not our work, but the work of the Dagestanis. Russia has been openly terrorizing Dagestan, it encircled three villages in the centre of Dagestan, did not allow women and children to leave," he said.

Here then is the perhaps the best provisional evidence of who was behind the bomb: a militant Dagestani group from Karamakhi, possibly connected to the Chechen fighters, but not acting on their orders.

Conspiracy theories

Meanwhile others in Moscow are still wondering whether there is a domestic political aspect to the crisis and whether rogue elements of the security forces are in some way involved in an attempt to provoke a state of emergency in Russia or the cancellation of elections.

Tough challenge for Moscow's popular mayor

There is absolutely no proof of this, but a little noticed article in the Moscow newspaper Moskovskaya Pravda by a respectable journalist Alexander Zhilin is now attracting attention.

Zhilin wrote on 25 August that President Yeltsin's health was failing and that a plan with the codename "Storm in Moscow" was being hatched in the Kremlin.

He wrote that "tremendous shocks await Moscow," including a series of terrorist acts, which were being designed to discredit the mayor of Moscow Yury Luzhkov and force a cancellation of the elections.

Conspiracy theories are part of the staple diet of Moscow politics.