Discretion is a virtue in the humanitarian aid industry and its workers do think carefully before speaking out in public on controversial matters.

However, the recent statement by a top Sri Lankan official that Action Against Hunger (Action Contre la Faim) (AAH) were responsible for the massacre of 17 of their own local staff last year through “negligence” and “irresponsibility”, deserves some sort of response.

The massacre, which happened a year ago, was the single largest act of mass murder perpetrated against aid workers since the Baghdad bombing of 2003.

There is a strong suspicion that it was carried out by Sri Lankan soldiers, but international observers are being increasingly branded as “terrorist sympathisers” for challenging the government’s security crackdown.

The government’s chief whip, Jeyaraj Fernandopulle, recently described the UN’s undersecretary general for humanitarian affairs, John Holmes, as “completely a terrorist, a terrorist who supports terrorism” after he spoke out about the safety of humanitarian staff.

I have a small personal interest in the case because I was one of the international aid workers who were “scrambled” to Sri Lanka after the Tsunami disaster of Christmas 2004.

Arriving in Sri Lanka the first thing that struck me was how peaceful it seemed. A truce had brought an end to the country’s long-running civil war and the main focus of my programme was to help resettle the people who had been displaced by this conflict.

I remember being reassured at my security briefing that no one regarded us “legitimate targets”. It soon no longer seemed strange to drive around Colombo in an open tuk-tuk or head into the field in a thin-skinned vehicle.

We no longer had to worry about the ethics of donning flak-jackets or accepting military escorts. We travelled freely through government and rebel controlled territory without even thinking about the need for special precautions.

I received a bit of a shock when I bumped into my successor at a seminar in Norway in June, last year.

A few weeks previously one of his national staff had been murdered just yards from an army checkpoint after he had refused to give a lift to some soldiers in one of our vehicles. The truce was collapsing and the country was sliding back into war. It was not difficult to recognise the symptoms of post-traumatic stress building up in my colleagues.

Since then 30 more aid workers have been murdered in Sri Lanka, making it probably the most dangerous place in the world for air workers to operate. The civil war has claimed over 4,500 lives during the same period with civilians caught, as ever, in the fighting between the two forces. There is now every indication that things are going to get worse.

Within this larger tragedy, it might seem self-interested to focus on the plight of aid workers, but attacks on them have a multiplier effect in terms of human suffering because it disrupts the delivery of life-saving relief. Hundreds of thousands of people have been displaced from their homes and now desperately need food and medical supplies.

For the past year AAH has been pressing for a full investigation into the murder of its staff. They were found in their own compound wearing T-shirts that identified them as humanitarian workers. They were lying face-down and it appears that they had been deliberately executed.

Ironically the latest statement, made by Rajiva Wijesinha, head of the government’s peace secretariat could actually be considered a step forward. Although he condemns AAH for their “utter irresponsibility” for “putting such workers at risk” he has at least called upon the minister for human rights to investigate the matter.

It is difficult to think of anywhere else in the world that such a scandal would have raised so little outcry. Sri Lanka’s brutal civil war has rumbled on for almost a quarter of a century attracting little attention from the outside world. But there are some red lines of inhumanity that governments should be told they cannot cross.