A UN document being circulated around diplomatic missions in Sri Lanka estimates that nearly 6,500 civilians have died and 14,000 have been injured.
The BBC's Charles Haviland, in Puthukkudiyiruppu near the front line
A jolting ride in armoured vehicles took us across the swathe of north-east Sri Lanka which until a couple of months ago was held by the rebels.
Buildings are badly damaged and the land is devoid of people. They've all been taken to areas the government calls welfare villages.
Then suddenly, in coconut groves, we saw a long line of people who've freshly fled from the conflict zone. Many looked seriously ill, and most very weak.
Surrounded by soldiers, people told us briefly that they'd been hungry or thirsty, or were happy to be out, or that the Tamil Tigers had prevented them from leaving. We and they were then moved on.
Meanwhile senior Indian officials have met Sri Lankan President Mahinda Rajapaksa in Colombo, following Foreign Minister Pranab Mukherjee's call to end the killing of civilians.
Indian National Security Adviser MK Narayanan told the BBC Sinhala service that he and Foreign Secretary Shivshankar Menon informed President Rajapaksa that they were concerned about the severity of the crisis.
"We expressed our concerns about the humanitarian situation as a result of nearly 100,000 Tamil civilians coming out of the conflict zone since early this week," he said.
"The president was receptive to our views and we hopeful of a positive outcome."
Brig Silva said intelligence reports indicated that Velupillai Prabhakaran and other rebel leaders were still in the conflict zone and appeared to be preparing to make a last stand.
He has not been seen for 18 months, and there was speculation that he was killed or fled the island.
The army says that two key rebel spokesmen who surrendered to troops earlier in the week had reported that Mr Prabhakaran was still in charge of his "cornered and depleted separatist army".
It says that rebels are now dressing in civilian clothing to blend in, and firing into the zone using heavy weaponry so people would think the army was firing at them.
But our correspondent says there is no way of verifying these reports.
On Thursday, the representative of the UN refugee agency (UNHCR) in Colombo, Amin Awad, called on the Sri Lankan government to allow pauses in the fighting so the necessary work could be completed.
"We are calling on the government to restrain itself and have the moral upper ground by allowing the humanitarian aid in, and we're asking the LTTE [Tamil Tigers] to open the gates of hell and allow these people out into safety," he said.
Hours earlier, UN Secretary General Ban Ki-moon announced the immediate despatch of the humanitarian team.
Thousands of people are caught with the Tamil Tigers in a 12 sq km (5 sq m) area in the north of the country as the military closes in.
The UN's humanitarian coordinator, Neil Buhne, said tens of thousands of people were living in camps in the northern town of Vavuniya.
"I saw infants with dysentery, malnourished children and women, untended wounds, and people dressed in the ragged clothing they've been wearing for months," the Associated Press quoted him as saying.
Paul McMaster, a British surgeon with Medicins Sans Frontieres (MSF), told the BBC a "continuous stream" of patients had been arriving at the hospital in Vavuniya since the weekend.
He said the hospital was equipped with 400 beds but was treating nearly 2,000 patients, many of them with gunshot wounds and blast injuries.
"We are doing emergency surgery, but the hospital is completely overwhelmed," he said, with patients lying on the floor, in corridors and outside under trees and temporary shelters.
On Thursday, Sri Lankan Defence Secretary Gotabhaya Rajapaksa rejected a UN appeal to allow aid agencies in.
While the government has allowed aid agencies to help those fleeing the conflict, Sri Lanka's UN ambassador says only the International Committee of the Red Cross (ICRC) and the Catholic charity, Caritas, have been let into the war zone itself.
On Wednesday the UN Security Council, which had been accused of inaction, called on the Tamil Tigers to lay down their arms and urged the Sri Lankan government to allow international aid agencies into areas of need.
The UN and Western nations - including the US and the UK - have been pressing for an immediate halt to the fighting to allow time for civilians to leave the war zone safely.
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