The Russian Health Ministry today belatedly identified the gas that killed more than 100 hostages at a Moscow theater during a rescue attempt last weekend as a powerful form of the opioid drug fentanyl.

The official acknowledgment, days after Western experts said they suspected fentanyl was the substance used, came as the hostage death toll from the effects of the gas rose by two, to 117. Moscow health officials said two other hostages were killed by gunfire during the 58-hour standoff with Chechen guerrillas that ended with a pre-dawn raid on Saturday.

In an evening news conference, Health Minister Yuri Shevchenko acknowledged that the gas was based on "derivatives" of fentanyl, a commonly used anesthetic, which he said was deployed to "neutralize the terrorists." Despite the large number of fatalities, he denied that doctors were ill-prepared to handle the consequences for the hundreds of hostages in the theater, and stressed that Russia's use of the gas did not violate the international treaty on chemical weapons, of which Russia is a signatory.

As a grieving city laid to rest at least 43 victims in funerals today, Danish authorities in Copenhagen arrested a top aide to Chechen separatist leader Aslan Maskhadov, saying he may have been involved in the Moscow hostage crisis and other terrorist attacks. The aide, Akhmed Zakayev, was detained late Tuesday, Danish authorities said, after attending the final session of the World Chechen Congress being held in the Danish capital -- a gathering that drew outrage from Russia for being held right after the Moscow theater siege. A Danish judge ordered Zakayev held until Nov. 12, pending investigation.

In Moscow, officials said they had rounded up dozens of suspects as possible accomplices. Meanwhile, politicians from the reformist Union of Right Forces party today lost their bid to open a special parliamentary commission to determine how such a large, heavily armed group of Chechens could have mounted a terrorist attack in the center of the Russian capital.

Many questions have also surrounded the gas, with some doctors and diplomats saying Moscow medical authorities were unprepared to handle the hundreds of casualties from the theater because of the government's desire to conceal details about the substance.

On Tuesday, U.S. Ambassador Alexander Vershbow joined the widespread criticism of the official secrecy and said the failure to inform Russian doctors about the gas may have cost lives.

At the news conference, Shevchenko denied that was the case. He said 1,000 antidotes for the gas had been on hand for use by medical personnel after the raid. He did not specify the chemical compounds in the gas or the antidote.

"Specialists, in particular myself, had been warned, even though the operation had to be carried out on short notice," he said. He denied reports from doctors who treated the hostages that said many more could have been saved if adequate resources had been available on the scene.

Shevchenko said the gas would not have killed the hostages had they not been weak from several days in the theater without proper food or medical care. "On their own, these substances cannot lead to a fatal outcome," he said.

At the same news conference, Moscow prosecutor Mikhail Avdyukov pledged a thorough investigation into the hostages' deaths. "We are not going to conceal anything," he said.

But for days following the raid, that is what Russian authorities did. They refused to provide details about the gas to doctors in Moscow hospitals treating the patients, barred hundreds of panicked relatives from seeing their loved ones and maintained a steadfast silence even after Western experts identified the gas.

For many observers here, such behavior has had echoes of the Soviet past. "We know the truth now, but it's too late to save the patients," said Lilia Shevtsova, a political analyst at the Carnegie Moscow Center. "It's a typical Soviet reaction, where the individual is nothing and the state is everything. Their assumption is that this is a state secret."

Russian doctors treating the hostages have also spoken out, saying the failure to prepare a better rescue plan led to many of the deaths. A leading Russian chemical arms expert, Lev Fedorov, said tonight that Shevchenko was also wrong when he said fentanyl was not deadly on its own.

"With fentanyl, as specialists say, the threshold of an admissible and inadmissible dose for a human organism is very close," he told NTV television. "Any mistake may be fatal."

According to U.S. experts, fentanyl belongs to a group of medicines called narcotic analgesics that suppress breathing. A normal dose goes to the brain but then is quickly redistributed to the rest of the body, making it a short-acting anesthetic. But a larger dose is not redistributed as easily, remaining concentrated in the brain and shutting down respiratory functions. The drug naloxone counteracts its effects, but would have to have been administered by Russian rescue workers almost immediately.