KABUL (Reuters) - Civilian casualties from the Afghan conflict dropped by almost a quarter in the first three months of the year, amid freezing winter weather and a sharp fall in the number of suicide attacks, the United Nations said in a report on Wednesday.

Overall civilian casualties fell to 1,773 in the January to March period, a 23 percent drop from the same period a year earlier, the latest report from the UN Assistance Mission in Afghanistan (UNAMA) said. That was made up of 581 killed and 1,192 wounded.

At the same time, the report pointed to the large number of casualties caused by U.S. and Afghan government air strikes, which killed 145 people and made up the largest single cause of civilian deaths during the period. It said 140 of those came from U.S. air strikes.

With overall casualties caused by militant groups down by more than a third over the period, for the first time since the UN began compiling records more than a decade ago, pro-government forces caused more deaths.

“A shocking number of civilians continue to be killed and maimed each day,” Tadamichi Yamamoto, the top UN official in Afghanistan, said in a statement calling on all sides to do more to protect civilians.

He said militant groups should stop deliberately targeting civilians and using improvised explosive devices (IEDs) such as roadside bombs, while pro-government forces should cut the rising death toll from air strikes and search operations.

While results from a single three=month period may be insufficient to demonstrate a broader trend, the figures reflect a slowdown in violence over an unusually cold winter with an especially big drop in the complex suicide attacks that have been a hallmark of the conflict.

UNAMA documented four suicide attacks that killed or wounded 178 civilians during the first three months of the year, against 19 incidents that resulted in 751 civilian casualties during the same period in 2018, the report said.

The decline in suicide attacks coincided with a series of meetings between U.S. diplomats and Taliban representatives aimed at establishing a basis for full peace negotiations to end more than 17 years of war in Afghanistan.

However, the report said it was unclear whether the drop in casualties was influenced by the talks or by any measures by parties to the conflict to protect civilians better.

It also noted that the comparison was affected by the fact that last year saw one of the deadliest attacks of the entire war, when almost 350 people were killed or wounded in a suicide blast in Kabul in January 2018.

While casualties caused by insurgent groups including the Taliban and Islamic State fell by 36 percent to 963, including 227 killed and 736 wounded, they still accounted for the largest number of civilian casualties overall in the quarter.

By contrast, casualties caused by pro-government forces rose by 39 percent to 608, made up of 305 killed and 303 wounded.