Russia is mourning those who died when troops stormed a theatre seized by Chechen gunmen, but the Kremlin is being criticised for the gas it used to disable the rebels - and which killed more than 100 of their captives.
The government has so far refused to name the gas which special troops used to knock out the rebels on Saturday morning before they could detonate explosives strapped to their bodies in the Moscow theatre they seized three days earlier.
US officials said this evening the gas Russian forces pumped into a theatre to end the hostage crisis was a deadly opiate.
A spokesman for the US Embassy spokesman in Moscow say doctors from a Western embassy have examined some of the former hostages.
The medics have concluded that "the agent they were exposed to appears consistent with an opiate rather than a nerve agent."
Russian officials have still refused to tell the US Embassy what exactly the gas was "despite repeated formal requests."
Moscow's top doctor Mr Andrei Seltsovsky says 646 hostages are still in hospital - 150 in intensive care, 45 of them in a grave condition.
Early reports on Saturday said only around 10 hostages had died, suggesting that the operation had been more successful than had first seemed possible.
But the death toll rose inexorably. During Saturday it hit 67, then over 90, before reaching 117 on yesterday. Only two died from gunshots. Asked what had killed the other 115, Mr Seltsovsky said succinctly: "The effects of the gas exposure".
The world's chemical weapons watchdog may be called on to investigate the use of lethal gas used to overcome the rebels, it emerged this evening.
Chemicals pumped into the building by Russian special forces may be banned under an international convention on chemical weapons and were likely to raise questions among members of the Netherlands-based Organisation for the Prohibition of Chemical Weapons, or OPCW, said officials.
President Vladimir Putin vowed today that Russia would make no deals with terrorists, Russian news agencies reported.
"Russia will make no deals with terrorists and will not give in to any blackmail," Mr Putin was quoted telling government ministers. The agencies also quoted Mr Putin as saying that Moscow would respond in "appropriate" fashion to any threat to use weapons of mass destruction against Russia.
Flags were ordered flown at half mast today and light entertainment was cancelled in the city of more than 10 million. Wednesday's Champions' League match in Moscow between Spartak Moscow and FC Basel was cancelled as a mark of respect.
Passersby placed fresh flowers and candles in plastic glasses outside the theatre where the hostages were held for three days by the Chechen suicide squad. Fifty, or nearly all of them, were killed in Sunday's assault.
President Putin apologised within hours of the pre-dawn operation on Saturday for proving unable to save all hostages.
But initial relief was replaced by doubts about the mysterious gas as the death toll mounted over the weekend.
"They poisoned us like cockroaches," a woman quoted her daughter as saying in Kommersant daily.
One doctor expressed frustration at being powerless to help survivors.
"I saw no gunshot wounds at all. Those who died had swallowed their vomit or their tongue or their hearts had stopped," he told one newspaper.
"If only we had known beforehand! If they had told us that we would be getting large numbers who had lost consciousness or heart failure, it might have been a bit different."
In a separate development, Chechen President Mr Aslan Maskhadov is prepared to hold unconditional talks with the Russian leadership to find a political solution to the bloody conflict in Chechnya, his envoy said today.
"We can only solve it politically," Mr Akhmed Zakayev, deputy prime minister of Chechnya, told the World Chechen Congress, which opened in Copenhagen despite Russian protests.
"President Maskhadov, as before, is ready without any preconditions to sit at the negotiation table. It is up to the Russian leadership," he said through an interpreter.
EU president Denmark said it had decided to move the venue of a November EU-Russia summit from Copenhagen to Brussels after President Putin had threatened to pull out to protest against Denmark's hosting of the Chechen meeting.