Russian emergency workers have recovered 322 bodies from a school in Beslan in North Ossetia that witnessed a hostage crisis involving more than 1,000 people for nearly three days.

At least 155 of those killed were children.

The air in Beslan smelled of smoke and gunpowder as the workers sifted through the landmine-laden school gymnasium searching for survivors and dead bodies.

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"Investigating operation are continuing, and the death toll will most likely go up as the de-mining operation is still in progress," Deputy Prosecutor Sergei Fridinsky said.

Russian troops were forced to storm the building on Friday after the terrorists started firing on the panicked hostages, who were running after two explosions in the gym, Fridinsky told the state-run Rossia channel.

Almost all the victims had blast injuries or bullet wounds in their back, proving that they were fired at while trying to flee, local government spokesman Lev Gudzayev said.

Carelessness on the part of the hostage-takers, quarrel among them or accidental pulling of the trigger were considered as possible causes of the blasts, ITAR-TASS said.

Officials said 27 hostage-takers and 10 Russian special forces were killed in the operation. Three captors were caught alive.

President Vladimir Putin, who visited the site, warned against succumbing to terrorists' provocation.

"The whole of Russia is worrying and mourning with you," he said as he visited the wounded and met the local authorities. "Nobody wanted to use force."

Putin said he had ordered the closure of the region's borders as a search operation was launched to nab the terrorists.

Russian news agencies, quoting local officials, said the siege was planned well in advance and the terrorists had smuggled arms into the school building when it was under renovation.

"We found a large amount of explosives and mines and their number says that this attack was planned well in advance," said Valery Andreyev, head of North Ossetian security service.

"When the explosions took place, children and adults rushed to the windows. And the terrorists went on a shooting spree. Even after the majority of people escaped from the gym, they continued to spray the bodies of dead," 34-year-old Alla Gadziyeva, a witness, said.

"If shooting had not begun, the hostages would have started to die of thirst and exhaustion," Gadziyeva said.

A schoolboy told NTV that they had to drink their urine on the second day of the hostage drama, as they were not allowed to go to the toilet, where there was a water tap.

In a related development, the authorities in Beslan were looking for an elderly man and a middle-aged woman who were trying to incite rioting and disorder in the city.

"They appear at places where relatives eagerly wait for news about their dear ones, and the moment police or security official start speaking, the elderly man and his woman accomplice start shouting, 'It's you who killed our children', and disappear from the spot," ITAR-TASS quoted police sources as saying.