ODESSA, May 20. /ITAR-TASS/. Many people who died in Odessa's Trade Unions House torched by militants from Ukraine's nationalist organization Right Sector and the so-called Maidan's self-defense, died of poisoning by unknown substance, head of the regional department of the State Emergency Situations Service Vladimir Bodelan told reporters on Tuesday.

He was speaking after a session of the parliament's Interim Investigation Commission which is looking into the mass murder of civilians. The commission had met behind closed doors.

"Some 80% died not of carbon monoxide poisoning or inhaling smoke. It was some other cause, which might be chloroform," Bodelan said.

Earlier, the regional emergency situations official said that thousands of attackers had not let rescuers to the scene for a long time, continuing to throw incendiary mixtures at the building and shooting at windows.

"Our rescuers carried out and led out more than 350 people. I won't go into political discussions of this event, yet cannot keep silent about the horror experienced by the rescued people when they found themselves downstairs," Bodelan said. "They were so badly beaten that those who were still in the building refused to come out."

On Monday, head of the Interior Ministry's investigation department Vitaly Sakal said 32 people in the Trade Unions House in Odessa had died of chloroform poisoning on May 2. "Chloroform was found in litter and soot sampled during inspection of the building. We're now determining where this substance came from," Sakal said. "Inhaling chloroform vapors arrests breathing which happened in our case. Thirty-two people did not die of high temperature."

According to the police official, chloroform had been kept in the Trade Union House for several days.

To conduct a new expert examination, Ukraine asked the Israeli Embassy in Ukraine to provide skilled experts.

Regional police said 12 people suspected of crimes during May riots were in custody. They included representatives of both conflicting sides. Six people injured in the riots remain in Odessa hospitals. Their lives are not in danger, doctors said.

Chairman of the Interim Investigation Commission Anton Kisse said that a hot line was open for all those who could shed more light on those tragic event. "It will give an objective picture of what happened in Odessa and the Luhansk and Donetsk regions and provide an answer about who provoked mass disturbances, what caused numerous deaths and who should be held responsible for the bloodbath," he said.

Riots in Odessa broke out during the march staged by Right Sector extremists sent by Kiev, football fans from Kharkiv and activists of so-called Maidan self-defense. They torched a tent camp in the Kulikovo field where signature-collection was underway in support of the federalization referendum and granting Russian the status of state language. Federalization activists fled to the Trade Unions House which the attacks set aflame, too. Forty-eight people died, and another 247 were injured.

Many Ukrainian politicians, including people's deputy Oleh Tsariov and deputy of the Odessa Regional Council Vadim Savenko said the real death toll was higher. They claimed that the tragedy had claimed 116 lives and that the authorities were hiding this fact.