The explosions, apparently set off unintentionally by the hostage-takers, turned the gymnasium into a mass of twisted metal, shattered bones and charred flesh, with at least 100 bodies scattered on the floor. After the blasts, half-naked children weak with thirst and many covered in blood ran crying from the burning building with their captors in pursuit.

"We were sitting next to the window and talking to each other. And then there were these two explosions. It deafened us, and as soon as the explosions sounded, the entire gym, the floors, the walls and the ceiling, were covered in blood," said Zaur Aboyev, 16. "And I knew it was time to run."

As Russian forces stormed the school complex and hunted for some of the hostage-takers who fled, the crack of gunshots and the deep boom of large-caliber weapons filled this small Caucasian town for hours. Russian officials said they killed 20 hostage-takers, arrested three, and believed three others were still at large. A furious mob killed at least one of the fleeing captors.

"Today has only brought death, nothing else," said Rimma Gazzayeva, who helped drag corpses — possibly of people caught in the crossfire — off the streets.

The militants who seized the middle school Wednesday on the first day of classes were believed to be separatists from the nearby republic of Chechnya, where guerrillas have been fighting for independence from Russia for a decade.

The violent end to the 56-hour siege stunned a nation reeling from a series of major terrorist attacks believed linked to Chechen separatists who have killed about 320 people in the past two weeks.

In addition to the school siege, 90 people died in the near-simultaneous downing of two airliners, an explosion near a Moscow subway station killed nine, and militant attacks on police and government police in Chechnya's capital left at least 19 dead.

Focus on Chechnya

Putin has long contended that Arab terrorist groups, including al-Qaida, have played a role in the violence in Chechnya, where a majority of people are Muslim. Russia's Security Service reported that 10 of the hostage-takers at the school were Arabs, a claim that, if substantiated, would boost Putin's assertions.

Russian authorities said yesterday that they believed the siege was masterminded by Chechnya's most notorious warlord, Shamil Basayev, an Islamic militant whose finances are believed linked with al-Qaida's.

President Bush condemned the bloodshed. "This is yet another grim reminder of the lengths to which terrorists will go to threaten the civilized world," he told a campaign rally in Wisconsin.

Hostages described three days of sweltering heat in the crowded gym with little food and less water. Many said they had resorted to drinking urine from their own shoes and chewing the leaves of houseplants at the school to relieve their thirst.

One boy, 10-year-old Stanislav Tsarakhov, said another boy was so thirsty he approached one of the hostage-takers who was holding an assault rifle with a bayonet attached. "The boy went to him and asked for a little water, and instead of giving him water, he drove his bayonet through the boy's body," Tsarakhov said. "I don't know if he died."

Tsarakhov's life may have been saved when a woman he had never met threw herself on top of him after the first big explosion, shielding him from the second. It is not known what happened to the woman.

The captives described three days of terror as the hostage-takers fired guns into the air to silence the constant crying of the children.

"They didn't allow us to sleep. They kept us awake all the time. They would pour our own urine on our heads," said 11-year-old Arsen Khasigov, whose mother had accompanied him to the school on Wednesday and was also taken captive.

"I got out because my mom threw me out the window," he said. "She's in the hospital now because some concrete blocks fell on her head. But she pushed me out of the window."

"The kids were crying all the time, almost all of them," said Serafima Bekoyeva, a 44-year-old kindergarten teacher who was held hostage with her two sons. "Because they were hungry. And how would you react if you were held by people who were waving their guns in your face and shouting at you, 'Shut up, you pigs.' ... They kept demanding that the kids stop crying, but how can you keep your kids quiet in such a situation? So they would start firing their guns in the air."

Russian authorities emphasized they had not planned to storm the school and were hoping to continue negotiations to bring the hostages out. But the situation spun out of control about 1 p.m., when a team arrived under an agreement negotiated with the hostage-takers to remove seven bodies that were in the courtyard since Wednesday.

"A blast came from inside the school just when rescuers were removing victims' bodies. Another several blasts closely followed in the heavily mined premises," said Valery Andreyev, head of the Federal Security Service in the republic of North Ossetia.

Chaos begins

What triggered the initial explosion is unclear. The leading theory is that one of the hostage-takers accidentally set off a booby trap, but some hostages suggested that an explosive accidentally fell off a basketball hoop in the gym. Others said a trip wire that had been taped to a wall was dislodged.

In any case, with many of the explosives electrically linked, the first blast set off at least one other, touching off a fire and causing the roof of the gym to collapse. A group of about 30 hostages began leaping for the open windows to escape. As they ran, their captors pursued them, shooting and battering them with their rifle butts.

The unexpected explosions and gunfire caused Russian commandos surrounding the school to open fire on the hostage-takers, and chaos ensued.

"I don't even realize to this moment how I managed to escape," said Bekoyeva, the kindergarten teacher. "There were deafening blasts all around us, and it was impossible to tell where they were coming from. We immediately started to push kids out the windows," she said.

Hostages described running through intense gunfire and hiding in a series of outbuildings before reaching a police command post.

As the gunfights raged, the hostage-takers split into three groups and two of them drifted or fought their way into the surrounding, heavily congested neighborhood, where Russian forces battled them among apartment buildings.

At Beslan's only hospital, ambulance after ambulance roared up the driveway, only to nearly collide with one of dozens of passenger cars that were approaching at breakneck speed to deliver victims.

Fathers roamed the streets nearby carrying their nearly naked and sometimes blood-speckled children. Many of the children had apparently taken off much of their clothing because of the stifling heat in the gymnasium.

A makeshift morgue nearby was a scene of intense grieving, as burned and broken bodies — many of them tiny — were brought in and laid out briefly for identification. The sound of wailing engulfed the hospital grounds, as men and women dropped to their knees, clutched their heads in grief and wept.

Inside the morgue, a middle-aged man with his arms covered in blood up to his elbows helped load bodies onto stretchers for transport. At one point, a jaw fell off with a click onto the tile floor. He picked it up and gazed dumbstruck at the crowd, a cigarette in his mouth and tears streaming down his face. Then he quietly placed the jaw next to the rest of the body and continued his work.

Battle continues

Closer to the school, Russian troops and police battled the militants for much of the afternoon, and the boom of tank fire occasionally sounded a bass note underneath the constant rhythm of small-arms volleys.

"Some of them (the terrorists) managed to escape from the school. But the area is cordoned off, and they don't have a chance," said one police officer attempting to keep hundreds of curious civilians away from the line of fire.

But a senior lieutenant with the Defense Ministry troops appeared less confident. "Nobody really knows how many fighters escaped," he said, adding that there were reports that some militants had dressed in civilian or medical personnel clothing. "God knows where these people are now. If we don't manage to snatch them out by dark, we're (in trouble)."

The speaker of the local parliament, Taimuraz Mamsurov, called on the public to "break into groups, take radios and mop up your living quarters — stop every man who doesn't live in that quarter." Within hours, the streets were filled with civilians toting their own rifles.

A few blocks away from the school, a man thought to be a fighter was killed by a mob shortly after he was arrested, according to witnesses.

"You could look at his face and see he was not an ordinary person. Everything he was wearing was black, and he had a long beard," said Vyacheslav Kudukhov, who watched the scene unfold. The man, he said, "kept yelling, 'I'm a correspondent!' But everyone knew he was lying."

"The crowd grabbed him. The police managed to seize him for a short time, but while they were escorting him, at some point one of the local people who had a hunting rifle just shot the guy in the chest," said Tatyana Sagutonova, a 22-year-old student who lives in a nearby building.

The most intense battle continued to focus on the school, where about three hostage-takers remained with as many as 50 hostages until Russian forces finally overcame what appeared to be the last of them last night.