Yesterday it emerged that a senior British army officer, Colonel Owen McNally, had been arrested under the Official Secrets Act for allegedly passing classified information to a human rights worker in Afghanistan. Unnamed sources suggested he had become "close" to the campaigner Rachel Reid. Here, for the first time, she responds to what she says is a "vicious slur"

According to news reports, Colonel Owen McNally has been flown back to Britain, where he will reportedly be interviewed by military police. The Ministry of Defence has told media that I was the recipient of these secrets as a researcher for Human Rights Watch.

Whatever the MoD has whispered into the ear of the Sun, Col McNally and I met only twice, both times in a purely professional capacity, both times at the Nato military HQ in Kabul. Both times we met to talk about civilian casualties from US and Nato air strikes.

What has happened in the last couple of days has been bewildering. I do not understand how these two meetings might have led the British government to accuse McNally of a serious crime that could lead to a hefty jail sentence, and why my government might want to see my reputation dragged through the mud, when I live in a country where a woman's reputation can mean her life. The meetings seemed unexceptional. A QC retained by Human Rights Watch has confirmed that the kind of information I received is not covered by the Official Secrets Act.

If the ministry had been seriously concerned that one of their officers was leaking information, why leak it to the media? Why was my name released to the media by the MoD, with a (nudge, nudge, wink, wink) libel that our relationship was "close"? They would know exactly what impression they were creating, and presumably decided that my reputation was expendable in order to ensure coverage of their "story".

Why did journalists from the Sun, the Times and the Mail write this as a story focusing on the MoD's entirely bogus suggestion that I had some kind of "relationship" with McNally? Why is it that my photograph was published? Why have journalists not been asking questions about why the MoD has been encouraging them to publish a vicious, false slur about me in order stop me from doing my job for Human Rights Watch in asking for information from the Nato official in charge of monitoring civilian casualties?

Clancy Chassay reports on the impact of civilian casualties on the Afghan population guardian.co.uk

Living in Afghanistan, where democracy, a free media, freedom of information and freedom of expression are still a faraway dream, I have developed a deep appreciation of the freedoms I grew up believing I had in Britain. I expect better from my own government and from the British media that I used to be a part of.

I am proud of the work I do in Afghanistan. I care deeply about civilian casualties, as should the Ministry of Defence. This is what they should be focusing their energies on, not impugning the reputation of a human rights worker or charging one of their officers for trying to explain to me the precautions that international military forces were taking to avoid killing Afghans.

I talk to Afghans in the south and east of the country where the conflict rages. They tend not to begin with the horrors of the Taliban and other insurgents. What they want me to hear first are their stories about the women and children bombed at a wedding party, the Qu'ran that was ripped up by foreign soldiers in a night raid, or the family shot dead in their car because they didn't understand orders in English to stop at a checkpoint. They are outraged and bewildered by the killings, in particular the air strikes. By UN estimates, more than 500 civilians were killed in air strikes in Afghanistan last year. The insurgents may have killed more than 1,000, but Afghans expect little from the Taliban.

The worst civilian casualty incident of last year took place in Azizabad, in a district called Shindand in the west of Afghanistan. In August 2008 the US launched a "kill/capture" operation, targeting a mid-ranking Taliban commander. The Afghan Independent Human Rights Commission says that at least 76 civilians were killed, 59 of whom were children. The UN put the civilian death toll above 90. Among the many photographs of the dead, one in particular has always stuck in my mind. It is of a young girl who looks as though she could be sleeping. But beneath the long lashes of her closed eyes is a line of shrapnel wounds. She was five years old, and she was called Kubra. And in that photograph you can glimpse how the last moments of Kubra's life must have passed.

The US military, whose forces carried out the air strike, was cold and dismissive about the reports of civilian dead. Initially they denied any casualties, later admitting five to seven civilian deaths. It was only weeks later, after video evidence emerged that they were forced to investigate again and revised the civilian death toll up to 33. Whatever the final figure, the death toll from this incident was shocking. The subsequent military denials compounded the fury that Afghans already felt about these deaths.

In a letter to US Secretary of Defence Robert Gates on January 15, Human Rights Watch sharply criticised the Pentagon investigation. I don't know what the McNally case is really about. If I had to guess I would say senior US and UK defence officials are angry about our forensic dissection of the Pentagon's investigation, which exposed reassurances about US and Nato commitments to avoid further civilian casualties as at least partially hollow.

If the military would hold its people to account for these terrible mistakes then human rights organisations would leave them alone. In the meantime, they should remember that this has nothing to do with individuals like me, and everything to do with little girls like Kubra.

• Letter: Response from the MOD

• Rachel Reid is Afghanistan researcher at Human Rights Watch