BESLAN, Russia - Commandos stormed a school today in southern Russia and battled separatist rebels holding hundreds of hostages, as crying children, some naked and covered in blood, fled through explosions and gunfire. At least seven people were killed and 400 wounded.

The extent of the casualties was not immediately known. Russia's Interfax news agency reported seeing around 100 bodies in the gymnasium where the hostages - reportedly up to 1,500 of them, mostly women and children - were held for nearly three days.

Thee agency also reported that dozens of people were killed when the school's roof collapsed amid explosions early in the day's violence.

Russian authorities appeared to have taken control of the school, and all the hostages were evacuated from the gymnasium. But gunfire rang out through the town for hours afterward, before ending in the afternoon.

About a dozen hostage-takers escaped, with the Interfax new agency reporting that they split into three groups to blend in with the hostages and took refuge in a home nearby. Tank fire was heard from the area of the house, Interfax said.

Alexander Dzasokhov - the president of North Ossetia, where the school is located - said the militants had demanded independence for the nearby wartorn region of Chechnya.

Huge columns of smoke billowed from the school, where windows were shattered, part the of roof was gone and another part charred. The scene around the school was chaotic, with people running through the streets and the wounded carried off on stretchers. An Associated Press reporter saw ambulances speeding by, the windows streaked with blood. Four armed men in civilian clothes ran by, shouting, "A militant ran this way."

Soldiers and men in civilian clothes carried children - some naked, some clad only in underpants, some covered in blood - to a temporary hospital set up behind an armored personnel carrier. One child had a bandage on her head, others had bandaged limbs. Some women, newly freed from the school, fainted.

The children drank eagerly from bottles of water given to them once they reached safety. Many of the children were only partly clothed because of the stifling heat in the gymnasium where they had been held since the militants took the building on Wednesday. The hostage-takers had refused to let food or water into the school throughout the standoff.

"I am helping you," a man dressed in camouflage told a crying girl. Women gathered around, trying to soothe her, saying "It's all right. It's all right."

Associated Press Television News footage showed the bodies of four children and a woman, and the ITAR-Tass news agency reported at least seven people killed, including five militants.

A nurse spread clean sheets on stretchers, and told AP that Russian officials expected "very many" wounded.

Regional emergency officials said 250 hostages were wounded, including 180 children. The head of a children's hospital in the regional capital of Vladikavkaz said five of the 68 wounded children brought there were in grave condition. Interfax reported more than 400 wounded, including hostages and local residents.

The chaos erupted on the third day of the hostage standoff in Beslan, a town of 30,000 in North Ossetia, a republic near the wartorn region of Chechnya.

It began after militants had agreed to let Russia retrieve the bodies of people killed early in the raid. Explosions went off as the emergency personnel went to get the bodies at around 1 p.m., and hostages took the noise as a signal to flee, officials said.

Militants opened fire on fleeing hostages and security forces returned fire. Once the hostage-takers sought to flee, commandos moved in.

The hostage takers' identities were murky. Lev Dzugayev, a North Ossetian official, said the attackers might be from Chechnya or Ingushetia. Law enforcement sources in North Ossetia and Ingushetia, speaking on condition of anonymity, said the attackers were believed to include Chechens, Ingush, Russians and a North Ossetian suspected of participating in the Ingushetia violence.

Insurgents fought an earlier war for Chechen independence, a conflict that ended in stalemate. In the years since, the rebels and their sympathizers have increasingly taken to assaults and attacks outside the tiny republic.

Negotiators said the hostage-takers had repeatedly refused offers of food and water througout the standoff.

"They are very cruel people, we are facing a ruthless enemy," said Leonid Roshal, a pediatrician involved in the negotiations. "I talked with them many times on my cell phone, but every time I ask to give food, water and medicine to the hostages they refuse my request."

The school seizure came a day after a suspected Chechen suicide bomber blew herself up outside a Moscow subway station, killing nine people, and just over a week after 90 people died in two plane crashes that are suspected to have been blown up by bombers also linked to Chechnya.

In 2002, Chechen rebels seized a Moscow theater, a standoff that ended after a knockout gas was pumped into the building, debilitating the captors but causing almost all of the 129 hostage deaths.

The militants had reportedly wired parts of the school with bombs and had threatened to blow it up if security forces moved in. There were conflicting reports of the number of hostages being held at the school. Officials had initially said about 350 - but some freed hostages among a small group freed Thursday put the number at about 1,500.

Today's assault came after several explosions boomed from the area and dozens of hostages fled the school. The militants reportedly fired at children who ran from the building, and unconfirmed reports said some of the hostage-takers, possibly including women bearing suicide belts, had fled during the chaos and may have taken hostages with them.

Women escaping the building were seen fainting and others, some covered in blood, were carried away on stretchers. After the escape, commandos assaulted the building.

Interfax said the school's roof had collapsed - possibly from the explosives some militants had strapped to their bodies. The militants had reportedly threatened to blow up the building if authorities tried to storm.

On Thursday, the militants had freed about 26 hostages, all women and children.

President Vladimir Putin had said that everything possible would be done to end the "horrible" crisis and save the lives of the children.