The White House has firmly pinned the blame for the deaths of civilians in the Moscow theatre siege on the Chechen rebels who took them hostage.

President George W Bush "understands it is the terrorists with whom the blame lies", spokesman Ari Fleischer said after 115 hostages died in Saturday's rescue operation.

A deadly mixture of religious and political fanaticism is being pursued

Tony Blair

News that nearly all of the victims had died from a controversial gas Russian troops used to subdue the Chechen suicide fighters inside has caused an outcry in Moscow. US Defence Department officials have described the gas as an opium derivative.

But Russian President Vladimir Putin's tough line was endorsed by the UK's prime minister on Monday who said there were "no easy, risk-free, safe solutions" in such a situation.

"I hope people will understand the enormity of the dilemma facing President Putin as he weighed what to do, in both trying to end the siege with minimum loss of life and recognising the dangers of doing anything that conceded to this latest outrage of terrorism from Chechnya," Tony Blair told Parliament in London.

Mr Blair linked the Moscow siege, in which the rebels portrayed themselves as Islamic warriors, to the wider war on terrorism and such events as the bomb attacks in Bali and the killing of an American official in Jordan.

"A deadly mixture of religious and political fanaticism is being pursued by those who have no compunction about taking human lives, no matter how innocent and little about losing their own," he said

As Russia held a day of national mourning on Monday, President Putin also talked of the threat from "international terrorism":

"Here and there around the world we hear of threats from terrorists of the use of means comparable to weapons of mass destruction."

Gas controversy

Despite its support for President Putin's hard line on the rebels, the United States has, along with other foreign states, asked Russia to explain how so many hostages died from the gas used by its special forces.

The gas gave us a fraction of a second to be the first to shoot

Sergei Goncharov former special forces commander

The Russian authorities have refused to name the gas used or provide an antidote, causing frustration among doctors charged with tending the survivors at Moscow hospitals.

Officials at the US Defense Department, quoting the US Embassy in Moscow, believe the gas was an opium derivative which dulls the senses and deadens pain but may also cause coma and death by shutting down breathing and circulation.

A Kremlin official told the Financial Times newspaper that the gas used was an anaesthetic which "in normal conditions would not lead to lethal results".

Russian officials have cited security reasons for refusing to name the gas.

But the BBC's diplomatic correspondent, James Robbins, says that if a chemical banned under the international Chemical Weapons Convention had been used, the Russians would risk another country demanding inspections of Russian chemical and military sites.

'No other way'

The security forces deny they acted recklessly, arguing that the militants were threatening to kill themselves along with their 800 hostages.

About 800 hostages were held for 58 hours

A former commander of Russia's Alpha special forces, Sergei Goncharov, defended his comrades' operation to save the hostages.

"The use of the gas gave us a fraction of a second to be the first to shoot and prevent hostage-takers from pressing the detonation button or connecting the wires - this is why the gas attack was carried out."

Many of the thousands of mourners who came to the theatre in southern Moscow on Monday to lay flowers agreed.

"There was no other way," said pensioner Lyudmila Yemelyanova.

"If the explosives inside the building had gone off then not only the theatre but all the neighbouring buildings would have been destroyed."

Doctors said 24 hostages remained in hospital in a critical condition on Monday evening and of the 115 killed, the bodies of 109 had been identified.

Up to 50 male and female Chechen militants, many of them with undetonated explosives still strapped to their bodies, were also killed during the rescue operation.

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