More than 6,400 Sri Lankan civilians have been killed and 14,000 injured in fighting between the army and Tamil Tiger rebels since mid-January, according to the United Nations.

The figures were not made public by the UN, but were circulated among foreign embassies in Colombo, the Sri Lankan capital, and released to the media by a foreign diplomat.

The UN's previous estimated death toll – released in similar circumstances a week ago – was 4,500.

According to its new figures, 6,432 civilians have been killed in the fighting since January 20 and another 13,946 have been wounded. There was no immediate comment from the UN's office in Colombo.

The new death toll emerged four days after the Sri Lankan army advanced into a "no-fire zone" where it has pinned down the last of the Tigers with tens of thousands of civilians.

It came as India sent Shiv Shankar Menon, its Foreign Secretary, and M. K. Narayanan, its National Security Adviser, to Sri Lanka to press for a ceasefire to allow the civilians to flee the zone.

The army, which says that it has rescued more than 100,000 civilians from the zone since Monday, admits that some may have been killed, but insists the number is much smaller.

It accuses the Tigers of shooting many civilians as they tried to escape – an allegation that has been backed up by some of those fleeing the five-square-mile area on the northeastern coast.

It has also shown aerial video footage, taken from a surveillance plane, which appears to show Tigers shooting dead several members of a crowd of civilians on a beach in the no-fire zone.

The Tigers deny shooting civilians and accuse the army of killing at least 1,000 non-combatants in shelling on Monday alone.

It is impossible to verify information from either side as the government has banned most independent reporters and aid workers from visiting the frontline. The Times has been refused a journalist’s visa for Sri Lanka since August.

However, aid workers on the ground say that civilians have been killed by both sides inside the no-fire zone. They have also warned of a bloodbath if the army continues with its offensive before the remaining civilians are evacuated.

Hillary Clinton, the US Secretary of State, accused the Sri Lankan Government on Wednesday of causing “untold suffering” and said that “the entire world is very disappointed”.

Ban Ki-moon, the UN Secretary-General, has ordered a UN humanitarian team to visit the no-fire zone immediately and Britain is sending a minister to Sri Lanka on Monday.

India has been less outspoken until now, despite having 63 million ethnic Tamil citizens.

Analysts say that Sonia Gandhi, the leader of the ruling Congress Party, is keen to see the defeat of the Tigers, who assassinated her husband, the former Indian Prime Minister Rajiv Gandhi, in 1991.

However, the coalition Government has come under mounting pressure from the Tamil community and is anxious not to lose its support in the country’s ongoing parliamentary elections.

"These killings must stop,” Pranab Mukherjee, India’s Foreign Minister, said in a statement as the two Indian officials were dispatched to Sri Lanka.

"The Sri Lankan Government has a responsibility to protect its own citizens and the LTTE [Tigers] must stop its barbaric attempt to hold civilians hostage."

The Tigers have been fighting since 1983 for an independent homeland for ethnic Tamils to protect them from discrimination by the ethnic Sinhalese majority.

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