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

The warning came as Russian forces continued air raids on what they say are rebel positions inside Chechnya after about 100 attacks were carried out over the weekend.

Moscow says four rebel bases connected to insurgency in neighbouring Dagestan had been wiped out in the raids.

Now Shamil Basayev is quoted by the French news agency as saying that his suicide battalion "would make a name for itself" if the attacks did not stop.

Basayev - who Russian blames for the rebel incursions - said he had recruited 400 volunteers "ready to die for their faith" but refused to give further details or possible targets.

Warlord: Accused of leading Dagestan rebels

Officials in the Chechen capital, Grozny, say ordinary civilians are the main victims of Russia's attacks.

A local journalist has told the BBC that 20,000 people have fled their homes in the past two weeks and volunteers are mobilising in preparation for a Russian invasion.

Moscow says it has deployed tens of thousands of troops in its campaign against Islamic militants who have made two incursions into Dagestan since August.

A senior general has refused to rule out using ground troops against rebels.

First Deputy Chief of the General Staff General Valery Manilov said: "We do not have the right to rule (out) any method of intervention to destroy terrorist units, their bases or their means of existence."

Islamic conspiracy

Earlier, Russia's Prime Minister Vladimir Putin said international Islamic forces in pursuit of mineral resources in the Caucasus were to blame for the fighting in Dagestan.

The BBC's Carrie Gracie: "Russia's leadership says it will fight terror with force"

Speaking on Russian television, Mr Putin said that "reactionary circles in some Muslim countries" had realised that forces within the neighbouring separatist republic of Chechnya could be channelled for geopolitical ends.

"An idea emerged to use Chechnya as some kind of virtual Caucasian dagger to slice Russia like a piece of butter," he said.

Islamists wanted to set up "a theocratic state" in Chechnya and some other republics which would stretch from the Caspian to the Black Sea.

Bombs in Russian cities have killed more than 300 people

Mr Putin said Russia would not allow any further break-up of the Russian Federation, warning that the consequences would make the recent fighting in Dagestan and bombings in Moscow "pale in comparison".

Moscow is currently attempting to seal the border of Chechnya. Russian television said a large number of armoured vehicles and artillery pieces had been sent to the region.

The military action follows steps taken to beef up security inside Russia following a series of bombings in which more than 300 people were killed.

Russian security forces have been maintaining a high profile on the streets of Moscow and are carrying out identity checks, apparently concentrating on people whose appearance suggests Caucasian origins.

Moscow blames the rebels for the blasts, an accusation denied by the Chechen authorities.