MOSCOW — Doctors said Sunday they still hadn't been told exactly what was in a mysterious knockout gas that killed 116 hostages after Russian special forces stormed a Moscow theater to free them from Chechen terrorists.

The chief Moscow city doctor says more than 150 hostages remained in critical condition after the operation, which at first had been seen as a triumphant rescue mission.

The physician in charge of the city's poison unit said troops did not tell medical authorities they had gassed the auditorium until the 750 hostages were brought out, most of them unconscious.

"But we didn't know the character of the gas," said Yevgeny Luzhnikov, head of the city health service Department of Severe Poisoning. The substance was described as akin to compounds used in surgical anesthesia.

Andrei Seltsovsky, the chief city physician, explained that the gas affected hearts and lungs. He said he had no information when asked about reports that the compound could cause vomiting that would choke unconscious victims.

"In standard situations, the compound . . . does not act as aggressively as it turned out to do," Seltsovsky said. "But it was used on people who were in a specific (extreme) situation for more than 50 hours. . . . All of this naturally made the situation more difficult."

The approximately 800 hostages were taken Wednesday night when an estimated 50 Chechen rebels stormed the theater during a popular musical. They demanded that Russia end its war in Chechnya.

The few dozen hostages who were well enough to be released Sunday could provide few clues as the the nature of the gas.

"We knew something serious was going to happen" when the gas started seeping into the hot auditorium that reeked of excrement, said Mark Podlesny as he walked out of Veterans Hospital No. 1 near the theater.

"I lost consciousness. Yes, there was a strange smell," said Roma Shmakov, a 12-year-old actor in "Nord-Ost," the musical in progress when the gunmen burst in at 9:10 p.m. Wednesday.

The gas mystery tainted the rescue mission, overlaying it with an aura of confusion and callousness. The impression was bolstered by scenes outside hospitals where the hostages were taken for treatment. Friends and family crowded the gates in futile efforts to learn if relatives or loved ones were inside.

Authorities gave out little information on hostages' identities, what hospital they were in or how they had fared through the ordeal.

Even diplomats had trouble finding information about the estimated 70 foreign citizens who were among the captives. U.S. consular officials searched the city's hospitals for one of the two American citizens known to have been in the theater. A second American was found recuperating in a city clinic.

Two foreign women — one Dutch and one Austrian — were known to have died.

Only on Sunday afternoon, more than 24 hours after the hostages were freed, did hospitals post complete or even partial lists of who they were holding.

Visits still were prohibited. Some people outside the gates saw their relatives waving to them from windows. "They are hostages again," one visitor shouted to the armed guards at Hospital 13, where about half the captives were taken.

Most of those who left the hospitals hugged those meeting them, then hurried to get out of the chilling rain and avoid a pulsing crowd of reporters and TV cameras.

Those who stopped to talk gave accounts of the ordeal that sometimes contradicted the official version.

Podlesny questioned Russian television footage that showed the captors' corpses in the theater amid liquor bottles and syringes. "They didn't drink, didn't smoke, didn't swear. They were very disciplined," he said.

Both Podlesny and Georgy Vasilyev, the producer of Nord-Ost, disputed Russian officials' statement that the gunmen had begun shooting hostages before dawn and prompting the special forces' to start their assault.

A total of 118 hostages where known to have died since the Chechens stormed the theater — 116 from the effects of the gas, one young woman shot and killed early in the standoff and one hostage shot Saturday morning shortly before the rescue raid.

President Vladimir Putin visited the special forces troops Sunday to congratulate them on the mission and declared Monday a national day of mourning. As troops that had surrounded the theater building began to withdraw, Muscovites placed flowers at the perimeter.

Many of the 50 assailants killed in the hostage-rescue mission died after being shot in the head, apparently while unconscious from the gas. The Federal Security Service said three other gunmen were captured, and authorities searched the city for accomplices or gunmen who may have escaped.

The chief Moscow prosecutor, Mikhail Avdyukov, said Sunday that three people had been arrested in Moscow on suspicion of helping organize and carry out the raid, the Interfax news agency reported.

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The attackers included 18 women, many of whom said they were war widows. The women had explosives strapped to their bodies, and mines were place throughout the building the terrorists threatened to blow the building to bits unless Putin agreed to withdraw troops from mainly Muslin Chechnya

Russian forces pulled out of Chechnya after a devastating 1994-1996 war that left separatists in charge. In fall 1999, Putin sent troops back in after rebels based in Chechnya attacked a neighboring region and after apartment-building bombings blamed on the militants killed about 300 people.

In 1995 and 1996, rebels seized hundreds of hostages in two raids in southern Russia near Chechnya, and dozens of people died in both cases, many of them killed when Russian forces attacked the assailants.