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BESLAN, Russia - More than 100 people were killed Friday in and around a Russian school as a three-day showdown between Russian security forces and suspected Chechen militants erupted in a bloody climax.

Amid a series of explosions, gunfire and screams of fleeing children, commandos stormed the building where militants strapped with bombs had held hundreds of captives since Wednesday. Most of the dead were children, and more than half of the 400 people hospitalized were students, Russian officials said.

Amid the chaos and rescue efforts, the Interfax new agency reported that three militants remained blockaded in the basement of the school, possibly including the head hostage-taker. An official said some children were still being held hostage in the building.

Russian officials said the violent conclusion was not part of a planned military operation, suggesting the events may have been triggered by the militants inside the school.

Reports from the scene varied on the numbers of hostages killed, although most reports suggested a gruesome toll.

Interfax said the building's roof had collapsed -- possibly from the explosives some militants had strapped to their bodies -- and that dozens were killed.

The Russian regional health minister said 409 people were wounded, including 219 children.

Russia's security chief said the storming of the school was not a planned operation.

"I want to point out that no military action was planned. We were planning further talks," the regional head of the FSB security service, Valery Andreyev, told RTR television.

Early news reports said the raid came after about 30 women and children broke out of the building, some bloodied and screaming.

Interfax said militants fired at children who ran from the building, and unconfirmed reports said some of the hostage-takers, possibly including women bearing suicide belts, may have taken hostages with them.

"Those children who remained in the school, in general, were not hurt," said a security official quoted by ITAR-Tass.

The firing subsided after about 45 minutes, but then kicked up again later. ITAR-Tass said the soldiers blew a hole in the building to help with the raid and other reports said some of the raiders had escaped, possibly taking children with them, and were fleeing Beslan.

The militants' demands had not been clear. Reports after the standoff began Wednesday said the attackers demanded the release of people jailed after attacks on police posts in June that killed more than 90 people in Ingushetia, a region between North Ossetia and the neighboring republic of Chechnya. However, officials said Thursday that the hostage-takers had not clearly formulated their demands.

Authorities estimated 15 to 24 militants held the school.

The militants' identity was also murky.

Lev Dzugayev, a North Ossetian official, said the attackers might be from Chechnya or Ingushetia.