What was Moscow siege gas?

Police have not been letting relatives into hospitals

There's growing anger in Russia over the use of gas in the military operation to end the Moscow siege. It was, at first, hailed as a great military success but as more details emerge there's now talk of a serious blunder.

It's been confirmed that all but two of the 117 hostages killed in the operation died from gas poisoning

Up to 50 Chechen rebels were killed during the attack.

It remains unclear how many died from the effects of the gas and how many were shot.

650 of the rescued hostages are still being treated in hospital for gas poisoning

195 of those are still in intensive care.

Breakfast talked to the following people:

Mike Yardley is a military analyst. He said:

Click here to watch our interview with Mike Yardley.

The key question is whether executions were beginning and that could have been the reason why soldiers charged in. The symptoms associated with BZ gas are: irregular heartbeat, vomiting, and fainting. BZ gas was developed by americans, it was used in Vietnam. It is non toxic, the soldiers weren't wearing protective clothes.

We also heard from the russian journalist Victor Orlik and to Steven Rose, Professor of biology at the Open University. They talked about the gas, the role the Russian President is taking, and the Chechen problem.

Click here to watch our interview with Victor Orlik.

Click here to watch our interview with Steven Rose.

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The Russian authorities are under renewed pressure to provide details of the gas used by troops storming a Moscow theatre.

They admitted on Sunday that almost all the hostages who died in the operation by special forces were killed by the poisonous substance.

Families and friends of those who died are also demanding that the Russian Government explain what happened when the building held by Chechen rebels was stormed.

President Vladimir Putin went on television late on Saturday to apologise for the deaths.

Many hostages remain in a serious condition

A day of national mourning has been declared across the country on Monday for the 117 hostages who died when the three-day siege was ended.

The head of Moscow's city health committee, Andrei Seltovsky, told journalists that only one of hostages held by Chechen gunmen died of gunshot wounds.

He said nearly 650 of the rescued hostages are still being treated for gas poisoning in hospital, of whom 150 were in intensive care while 45 remained in a critical condition.

Up to 50 Chechen rebels were killed during the attack, but it remains unclear how many of them died from the effects of the gas, and how many were shot dead.

US demand

General relief that the siege of the Moscow theatre was over has given way to mounting concern about the methods used.

The Russian refusal to say which type of gas was used has irritated several western embassies in Russia.

The United States has officially asked for more information, insisting it is crucial for the treatment of casualties.

Questions remain over where the hostage takers came from

One Russian expert said the gas used was a chemical weapons agent and blamed the high number of deaths on delays in administering the antidote.

Lev Fyodorov, president of Russian's Union for Chemical Safety, told the BBC: "This was a military operation using non-lethal chemical weapons developed during the Cold War.

"They would have been intended for a military opponent."

As such, Mr Fyodorov said the authorities would be unable to prevent deaths of civilians in an enclosed space like the theatre.

The gas was pumped into the theatre complex to overcome the rebels before special forces went in.

However the gas also killed or incapacitated many of the hostages, leaving some unconscious, with breathing problems and memory loss.

Doctors said its effects resemble that of a general anaesthetic used in high doses.

Click here for more on the controversy about what kind of gas was used

Putin praised the operation which ended the siege

Distraught families have been clamouring for information about relatives who are being held at medical facilities across Moscow.

Police believe some of the Chechen rebels might be posing as civilian victims and want to screen all the patients.

However some former hostages who survived were released from hospital number 13 in Moscow on Sunday, amid tears and shouts of joy.

A large group of friends and family had gathered in the pouring rain to meet them, some clutching flowers.

For many, it was the first time they had seen their loved ones since they left for a performance of a popular musical at the theatre last Wednesday night.

The BBC's Sarah Rainsford in Moscow says the former hostages looked bewildered but walked unaided.

They reported sickness and headaches from the gas, but most said the worst had already passed.