MOSCOW -- The gas used by Russian commandos in their assault on a Moscow theater killed all but one of the 118 hostages who have perished so far, Russian health officials said Sunday night.
And the death toll, they said, was bound to rise.
Nearly 650 poisoned hostages remained hospitalized Sunday night. Moscow's chief physician, Andrei Seltsovsky, said 150 of the hostages were still in intensive care, 45 of them on the critical list.
Russian officials initially said 69 hostages had been killed, and they insisted that none of the deaths were caused by the gas.
As the death toll continued to rise Sunday, anguished families waited in bitter cold and a steady rain, pressing against the wrought-iron gates of Clinical Hospital No. 13, desperate for news about daughters, wives, sons and husbands.
A U.S. embassy official said an American woman and a U.S. green-card holder had finally been located in local hospitals, although he gave no personal details. Consular officials continued to search for at least one other American believed to have been a hostage.
A group of 54 Chechen militants, 50 of whom were killed in the siege, had taken over the theater on Wednesday night. Their single ransom demand was the immediate withdrawal of Russian troops from Chechnya.
Then in a pre-dawn raid Saturday morning, Russian troopers pumped the gas into the theater before storming it. The rebels apparently shot and killed just one hostage as the commandos moved in.
Most died in hospitals
There were numerous, unverified reports of semi-conscious hostages having choked to death on their own vomit inside the theater due to the gas attack. Health officials said Sunday that most had died in various hospitals from respiratory distress and heart attacks.
Russian officials refused Sunday to specify the exact name of the gas. Foreign diplomats have demanded information about the gas from the government, but without reply.
A physician involved in treating the hostages called the gas "a general anesthetic." He said heavy doses could cause "unconsciousness, respiration and blood-circulation problems."
The gas was powerful and fast-acting enough that the rebels -- including 18 Chechen women who had explosives wired to their bodies -- were unable to detonate the numerous bombs and mines they had placed around the theater.
One hostage described the gas as bluish-gray, and another said it was bitter-smelling. The Interfax news agency quoted an unnamed hostage as saying he saw one of the militants trying to put on a gas mask as the siege unfolded.
"He made several convulsive moves, trying to pull the mask over his face, and fell," the source said.
He also described how a fellow hostage, a teacher, had pressed wet napkins to her students' mouths during the ordeal.
"She kept the napkins that way until she lost consciousness," he said. "She saved the children."
President Vladimir Putin declared Monday a national day of mourning, with flags to be flown at half-staff. Putin also asked TV networks, radio stations and cultural centers to cancel their entertainment programs.