Sri Lanka yesterday faced fresh calls for a war crimes inquiry after reports in The Times that at least 20,000 Tamils were killed, mostly by army shelling, in the closing stages of the civil war. But as Colombo clumsily denounced the reports and the photographic evidence as propaganda, evidence has emerged that not only the United Nations but several Western governments knew of the slaughter weeks ago but kept silent for fear of upsetting the Sri Lankan Government. Such a monstrous collusion in covering up an atrocity must not go unchallenged. If the UN Human Rights Council refuses to investigate what has happened, the West must do so forthwith.

An abashed UN yesterday admitted that the death toll from Sri Lanka's civil war was “unacceptably high”. But spokesmen still refused to confirm the total, compiled from UN sources on the ground. The figures were based on meticulous reports of the daily deaths among the desperate civilian refugees hit by army shells, and the UN rebuffed Sri Lanka's claim that not a single civilian had been killed by shelling. The “well-informed estimates” of casualties, it said, had been passed on to governments and the UN had been “ringing the alarm bells” for a long time.

Those bells were certainly muted. No Western government made public the scale of the killing. Ban Ki Moon, the UN Secretary-General, flew over the beaches where thousands of bodies are buried in fresh graves. But he has yet to speak out on the slaughter or confirm the authenticity of pictures ludicrously described in Colombo as “fakes”. Has no one learnt the lessons of My Lai or Srebrenica? If diplomats and top UN officials are too timid to denounce atrocities as they take place, what hope is there of preventing future efforts at extermination?

To the charge that the West, and this newspaper, is playing down the atrocities of the Tamil Tigers or belittling Colombo's success in eliminating the terrorist threat, there is a clear retort: nonsense. For years the West and The Times have denounced the suicide bombings, assassinations, recruitment of child soldiers and terrorist violence that were the hallmark of this blinkered and ruthless organisation. The Tigers were proscribed as terrorists across Europe. Their uncompromising commitment to violence and intimidation of their compatriots abroad were denounced. The Sri Lankan Government's success in freeing the country of their ravages is not in question.

But callousness, indifference to civilian casualties, triumphalism and mass internment of civilians have been the price of victory. The Government clearly believed that the war would be more easily won if no one was able to witness the tactics. That temptation appeals to every military commander. And where governments have backed them, as in Chechnya or Gaza, the results have been horrific, the country's name has been stained and the body politic has been damaged by the tolerance of the intolerable.

The casualties of wars deliberately waged out of sight of reporters, doctors and diplomats are not only higher, but they include also the victors. Sri Lanka's determination to exterminate the Tamil Tigers behind a wall of secrecy will have made ostensible military sense, but at the price of deserved obloquy for a debased cause.

Warfare can never be sanitised and civil wars are especially vicious. But countries and governments fighting for their rights must allow as much transparency as possible about their aims and methods. To embed journalists with the armed forces may give only a partial picture, but this tells more of the truth than blanket censorship. Where there has been excess, it must be exposed - if only to give reconciliation a chance. The UN must cry out.