Washington(CNN) Afghan government, US and international forces have been responsible for more civilian deaths in Afghanistan in the first three months of 2019 than the Taliban and ISIS, according to a United Nations report out Wednesday.

This marks the first time since 2009, when the UN Assistance Mission in Afghanistan began documenting civilian deaths and injuries, that the number of deaths caused by pro-government forces during the first quarter of 2019 surpassed those the UN attributed to insurgent groups.

According to the UN report, the Taliban, ISIS and other insurgents were responsible for the majority of civilian casualties, which include deaths and injuries. Overall, the number of casualties saw a 23% decrease from the first quarter of 2018, the UN found.

The terrorist groups killed 227 civilians and injured 736 more in the first quarter of 2019, according to the UN.

In that same period, pro-government forces caused 305 deaths and 303 injuries among civilians -- a 39% increase from 2018's first quarter, the report notes.

From January to the end of March, 581 Afghan civilians were killed and 1,192 civilians suffered injuries, according to the UN. It was the lowest for a first quarter period since 2013, the UN said.

The UN attributed the lower number of civilian casualties to the decrease in suicide bombings, which it said may have been due to the "particularly harsh winter conditions" during that time.

"It is unclear whether the decrease in civilian casualties was influenced by any measures taken by parties to the conflict to better protect civilians, or by the ongoing talks between parties to the conflict," the report stated.

The three leading causes of civilian casualties were ground engagements (35%), improvised explosive device attacks (28%) and aerial operations (13%), according to the UN.

In a change in trends, non-suicidal IED attacks resulted in more casualties than suicide bombings in the first quarter, the report said. The UN documented four Taliban suicide bombings in the first quarter of 2019, compared to 19 bombings during the same period last year.

While it was the third leading contributor to overall casualties, aerial operations led to the most civilian deaths this period, the UN found. The report said 145 civilians were killed over 43 aerial operations conducted in the first three months of 2019.

Women and children made up half of the civilian casualties from all aerial operations, according to the report.

"A shocking number of civilians continue to be killed and maimed each day. All parties must do more to safeguard civilians," Tadamichi Yamamoto, the UN special representative for Afghanistan, said in a statement.

Yamamoto called on pro-government forces to "take immediate measures to mitigate the rising death toll and suffering caused by air strikes and search operations."

The US has approximately 14,000 troops deployed to Afghanistan, with the majority of those forces serving in non-combat roles as part of the NATO-led training mission, helping to train and advise local Afghan forces.

A defense official told CNN in December that President Donald Trump decided to withdraw about half of the US troops from Afghanistan.