Patients being evacuated from the makeshift hospital in Putumattalan. The International Committee of the Red Cross has evacuated more than 4,000 wounded and their caretakers from the war zone. However, new patients arrive at the hospital every day.

War is an exquisite breeding ground for euphemism. In Sri Lanka, a government announced "no-fire zone" in the northeast of the country is instead one of the most dangerous places on earth. Advertised as a place where trapped civilians could flee to safety from fighting between the army and the Tamil Tigers, this tiny strip of land has become a killing ground where the Tigers – facing defeat in their 25 year war for independence – use tens of thousands of Tamil civilians as human shields, physically preventing them from escaping to safety, while the Sri Lankan army shells the area with devastating consequences.

It is a scene out of Dante's Inferno. Heroic doctors short of supplies tend to hundreds of shell-shocked wounded, who lie on the ground in open air "hospitals," often caked in dirt and soaked in blood. Parents wail and children wander around dazed. The lucky ones receive emergency care, though sometimes this has meant amputations without anaesthetics. Victims have described shells or rocket propelled grenades landing while they slept.

One witness told us at Human Rights Watch that while he and hundreds of civilians were waiting in line near a food distribution centre, four or five artillery shells hit the area, killing at least 13 civilians immediately and wounding over 50 others. A doctor who examined the site two hours after the attack said that the shells were 120mm rounds and appeared to have been fired from Sri Lankan army positions to the south.

The Sri Lankan government has angrily denied reports that it has used artillery and other heavy weapons to attack the "no-fire zone." Yet today President Mahinda Rajapaksa's office announced that it had instructed the army to stop what it claimed it had not been doing: "Our security forces have been instructed to end the use of heavy calibre guns, combat aircraft and aerial weapons which could cause civilian casualties." At the same time, the government again refused calls by the US, UK, and others for a pause in the fighting. More unnecessary suffering will be the result.

The UN estimates that since January more than 6,400 civilians have died and almost 15,000 have been injured. But the figure could be much higher, as the government has refused to allow independent observers into the area "for their own safety." In a rare statement, the director of operations for the International Committee of the Red Cross said last week that he could not recall a situation in recent years as painful and extreme.

You might have expected that governments around the world would have done all they could to alleviate so much pain and suffering. Not a bit of it. The UN security council has done virtually nothing. With their veto power, China and Russia have blocked any concerted council action or pressure. Instead of acting, council members have spent a great deal of time wrangling over whether to hold private briefings on Sri Lanka in the UN's basement – which would make the meeting unofficial – or in regular council rooms.

And what of the UN Human Rights Council? There has been no special session demanding an end to the atrocities, no special envoy sent to warn of the risk of prosecutions if war crimes are committed. The reality is that although human rights and humanitarian organisations, together with some courageous diplomats and UN officials have been warning for months that the situation would reach this stage, governments have ignored them. The cost in civilian lives and suffering has been enormous.

This week, David Miliband, the foreign secretary, will travel to Colombo with the French and Swedish foreign ministers. The Sri Lankan government, riding high as the end of the Tigers' military campaign appears imminent, will remain obstinate, claiming that it is a democracy fighting terrorism and must be allowed to finish the Tigers off. But the message to Colombo must be clear. There will be a reckoning. Investigations into the conduct of the conflict by both sides will take place. The truth will come out. A commission of inquiry will be established. Tamils streaming out of the conflict area can no longer be treated as criminals and held in detention camps indefinitely. Humanitarian aid and independent observers must be allowed in immediately. And there must be no retribution, as Sri Lanka's defence secretary has suggested, against those considered disloyal to the government.

There is still time for the members of the UN security council and other countries to put people over political gamesmanship and allow the UN to finally bring its full and collective weight to protect some of the world's most vulnerable people. There is still time for the Sri Lankan government to show some respect for the rule of law, some tolerance towards critical voices from the Tamil community, and a vision for a political settlement that would make Tamils believe that Sri Lanka is also their country.

Brad Adams is Asia director at Human Rights Watch.