Those killed or injured fell by 15% in the first half of 2012 compared with the same period last year.
Analysts say increased sensitivity on both sides about the impact of civilian deaths in Afghanistan has led to more carefully targeted attacks.
“In the first six months of 2012, the armed conflict in Afghanistan continued to take a devastating toll on civilians,” the United Nations Assistance Mission in Afghanistan (Unama) report said.
Civilian casualties have risen steeply every year for the past five years – until this one.
The numbers are still high. More than 1,100 people were killed or injured in the first six months of the year – far more than three or four years ago.
Almost a third of the casualties were women and children.
And it may also be premature to talk about a new trend.
But the fact the numbers have fallen at all is significant and begs the question: Why? Taliban attacks against Nato-led forces have actually increased in recent months so it is not simply about the level of violence.
But both sides, pro- and anti-government, have become increasingly sensitive in the past few years about the impact of civilian casualties on public opinion. In the broader battle for hearts and minds, it is a key factor.
That awareness has caused shifts in tactics. The Taliban are trying to make their attacks more targeted, focusing more on checkposts and military bases and less on markets and public gatherings.
“Between 1 January and 30 June 2012, conflict-related violence resulted in 3,099 civilian casualties or 1,145 civilians killed and 1,954 others injured, a 15% decrease in overall civilian casualties compared with the same period in 2011,” it said.
The report emphasises however that while the reduction of civilian casualties “reverses the trend in which civilian casualties had increased steadily over the previous five years”, Unama remains concerned that the number of civilian deaths and injuries “remains at a high level”.