A suspected Chechen terrorist was arrested in Moscow carrying 18 pounds of mercury — a poison — while allegedly planning a new attack, and Russian officials said Thursday evidence implicated the top Chechen elected leader in last week's hostage siege in a Moscow theater.

Sergei Krym-Gerei, an alleged member of prominent Chechen warlord Shamil Basayev's gang, was carrying the mercury in a bottle when arrested. He has refused to answer questions.

"Such an amount of mercury would poison a very large number of people," city police spokesman Filipp Zolotnitsky said on NTV television.

The 36-year-old Krym-Gerei, from Russia's North Caucasus region, was detained several days ago by police acting on a tip, he said.

Meanwhile, a Kremlin spokesman said Thursday the leader of the Chechen hostage-takers, Movsar Barayev, was heard on intercepted telephone coversations saying he acted on orders from top rebel leader Shamil Basayev, who in turn was carrying out an order from separatist president Aslan Maskhadov. Barayev was killed in the hostage rescue operation.

Officials at a Thursday news conference played tapes of conversations between the hostage-takers and their contacts outside the theater less than three miles from the Kremlin.

Rebels stormed an Oct. 23 performance of the musical Nord-Ost, demanding an end to the war in the breakaway republic. They held about 750 people hostage for 58 hours until security forces ended the siege by pumping a knockout gas into the auditorium.

In two of the intercepted Chechen-language calls, which were translated into Russian, a voice identified as Barayev's said "Aslan" gave his blessing to the operation.

"There was other clear evidence that Mr. Maskhadov was fully aware of the developments and the people in the hall acted with his knowledge," Kremlin spokesman Sergei Yastrzhembsky said, though he did not offer further proof.

Yastrzhembsky also confirmed that Maskhadov had been placed on an international wanted list.

Moscow has sought to erase any distinction drawn by foreign governments between rebel warlords such as Basayev and those also serving as political representatives, including Maskhadov and his aides.

On Wednesday, Denmark authorities arrested Akhmed Zakayev, a key Maskhadov aide attending an international Chechen conference. Russia has requested Zakayev's extradition and alleges he was involved in the hostage-taking and other terrorist attacks.

"It is our deep conviction that the events in Moscow were tied with the plans of the organizers of the conference in Denmark," Yastrzhembsky said. "The political and military wings of the terrorists acted in unison."

The government also placed top Chechen political representative Zelimkhan Yandarbiyev, reported to be in Qatar, on an international wanted list, Yastrzhembsky said.

The alleged evidence against Maskhadov and Zakayev essentially ruled out any peace negotiations over Chechnya, Yastrzhembsky said.

"We can see that the image of Maskhadov — even in the eyes of those who pushed Moscow toward negotiations with Maskhadov — has seriously paled," he said.

"Name one leader [in Chechnya] with whom we could negotiate. I don't know of any such person."

In another intercepted call played at Thursday's news conference, Abu Bakar, earlier identified in media reports as Barayev's deputy, claimed his band had more than 100 accomplices around the Russian capital ready to carry out suicide attacks.

Yastrzhembsky said that claim could have been false and intended to frighten authorities because hostage-takers were aware their calls were being monitored.

The news conference came a day after Russia's health minister confirmed that a powerful opiate was used to subdue the attackers during the storming.

At least 117 people, not including the assailants, died as a result of the use of the aerosol compound, based on the fast-acting opiate fentanyl, which was pumped through the building's ventilation system before special forces stormed the theater early Saturday.

Some 184 former hostages remained hospitalized Thursday, with eight of them in serious condition, the Interfax news agency reported.

Health Minister Yuri Shevchenko said Wednesday the compound itself was not lethal, but became so when used on people starved of oxygen, dehydrated, hungry, unable to move adequately and under severe psychological stress.

However, injected, skin patch and oral doses of fentanyl sold in the United States carry warnings that the anesthetic can be fatal if administered in too high a dose, and doses must be customized according to the patients' size and any previous exposure to similar drugs.

Meanwhile, Chechens living in Moscow complained of increased harassment following the theater siege and said police were making unannounced visits to their homes.

Elita Usmanova, 33, said police armed with automatic rifles showed up at her apartment and took her two teenage sons to the local police station, where they were photographed, fingerprinted and questioned for several hours before being released.

She said she was afraid to let her children go to school or leave the apartment, for fear they would be detained again or attacked on the street.

"Friends called and said it's better to stay home. The police are stopping women and children, there's no difference," she said.